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 $55.68   11.571%   $62.1227   $62.12   $62.10   $62.10  
  Purchase #2 $151.32   10.823%   $167.6974   $167.70   $167.70   $167.70  
  Purchase #3 $232.26   9.177%   $253.5745   $253.57   $253.55   $253.60  
  Purchase #4 $158.67   8.854%   $172.7186   $172.72   $172.70   $172.70  
  Purchase #5 $231.61   13.209%   $262.2034   $262.20   $262.20   $262.20  
  Purchase #6 $15.94   4.257%   $16.6186   $16.62   $16.60   $16.60  
  Purchase #7 $79.88   13.835%   $90.9314   $90.93   $90.95   $90.90  
  7 purchase totals = $925.36       $1,025.8666   $1,025.86   $1,025.80   $1,025.80