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 $166.49   8.257%   $180.2371   $180.24   $180.25   $180.20  
  Purchase #2 $131.97   4.160%   $137.46   $137.46   $137.45   $137.50  
  Purchase #3 $124.71   9.142%   $136.111   $136.11   $136.10   $136.10  
  Purchase #4 $153.40   9.680%   $168.2491   $168.25   $168.25   $168.20  
  Purchase #5 $45.46   6.237%   $48.2953   $48.30   $48.30   $48.30  
  Purchase #6 $145.47   4.319%   $151.7528   $151.75   $151.75   $151.80  
  Purchase #7 $96.46   13.218%   $109.2101   $109.21   $109.20   $109.20  
  7 purchase totals = $863.96       $931.3154   $931.32   $931.30   $931.30