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 $55.97   5.229%   $58.8967   $58.90   $58.90   $58.90  
  Purchase #2 $102.69   11.773%   $114.7797   $114.78   $114.80   $114.80  
  Purchase #3 $95.30   12.192%   $106.919   $106.92   $106.90   $106.90  
  Purchase #4 $147.54   12.706%   $166.2864   $166.29   $166.30   $166.30  
  Purchase #5 $59.38   7.305%   $63.7177   $63.72   $63.70   $63.70  
  Purchase #6 $207.75   11.673%   $232.0007   $232.00   $232.00   $232.00  
  Purchase #7 $66.55   12.553%   $74.904   $74.90   $74.90   $74.90  
  7 purchase totals = $735.18       $817.5042   $817.51   $817.50   $817.50