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 $149.42   4.734%   $156.4935   $156.49   $156.50   $156.50  
  Purchase #2 $148.44   4.142%   $154.5884   $154.59   $154.60   $154.60  
  Purchase #3 $6.87   3.295%   $7.0964   $7.10   $7.10   $7.10  
  Purchase #4 $76.45   8.156%   $82.6853   $82.69   $82.70   $82.70  
  Purchase #5 $68.79   9.672%   $75.4434   $75.44   $75.45   $75.40  
  Purchase #6 $170.30   11.135%   $189.2629   $189.26   $189.25   $189.30  
  Purchase #7 $97.49   9.110%   $106.3713   $106.37   $106.35   $106.40  
  7 purchase totals = $717.76       $771.9412   $771.94   $771.95   $772.00