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 $48.62   4.823%   $50.9649   $50.96   $50.95   $51.00  
  Purchase #2 $87.53   11.221%   $97.3517   $97.35   $97.35   $97.40  
  Purchase #3 $208.91   9.831%   $229.4479   $229.45   $229.45   $229.40  
  Purchase #4 $203.96   4.651%   $213.4462   $213.45   $213.45   $213.40  
  Purchase #5 $72.62   3.475%   $75.1435   $75.14   $75.15   $75.10  
  Purchase #6 $212.54   6.424%   $226.1936   $226.19   $226.20   $226.20  
  Purchase #7 $95.87   5.285%   $100.9367   $100.94   $100.95   $100.90  
  7 purchase totals = $930.05       $993.4845   $993.48   $993.50   $993.40