Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $107.29   12.471%   $120.6701   $120.67   $120.65   $120.70  
  Purchase #2 $204.25   11.382%   $227.4977   $227.50   $227.50   $227.50  
  Purchase #3 $242.32   10.695%   $268.2361   $268.24   $268.25   $268.20  
  Purchase #4 $211.60   9.278%   $231.2322   $231.23   $231.25   $231.20  
  Purchase #5 $113.29   12.659%   $127.6314   $127.63   $127.65   $127.60  
  Purchase #6 $169.71   5.809%   $179.5685   $179.57   $179.55   $179.60  
  Purchase #7 $201.82   12.236%   $226.5147   $226.51   $226.50   $226.50  
  7 purchase totals = $1,250.28       $1,381.3507   $1,381.35   $1,381.35   $1,381.30