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 $154.50   11.711%   $172.5935   $172.59   $172.60   $172.60  
  Purchase #2 $212.99   8.695%   $231.5095   $231.51   $231.50   $231.50  
  Purchase #3 $69.59   8.260%   $75.3381   $75.34   $75.35   $75.30  
  Purchase #4 $162.74   12.869%   $183.683   $183.68   $183.70   $183.70  
  Purchase #5 $150.98   8.113%   $163.229   $163.23   $163.25   $163.20  
  Purchase #6 $120.89   13.108%   $136.7363   $136.74   $136.75   $136.70  
  Purchase #7 $45.42   12.863%   $51.2624   $51.26   $51.25   $51.30  
  7 purchase totals = $917.11       $1,014.3518   $1,014.35   $1,014.40   $1,014.30