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 $45.28   8.114%   $48.954   $48.95   $48.95   $49.00  
  Purchase #2 $18.69   6.451%   $19.8957   $19.90   $19.90   $19.90  
  Purchase #3 $154.39   12.699%   $173.996   $174.00   $174.00   $174.00  
  Purchase #4 $27.59   4.652%   $28.8735   $28.87   $28.85   $28.90  
  Purchase #5 $25.71   13.343%   $29.1405   $29.14   $29.15   $29.10  
  Purchase #6 $207.65   7.533%   $223.2923   $223.29   $223.30   $223.30  
  Purchase #7 $213.29   11.122%   $237.0121   $237.01   $237.00   $237.00  
  7 purchase totals = $692.60       $761.1641   $761.16   $761.15   $761.20