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 $61.71   5.565%   $65.1442   $65.14   $65.15   $65.10  
  Purchase #2 $246.85   7.370%   $265.0428   $265.04   $265.05   $265.00  
  Purchase #3 $194.81   6.454%   $207.383   $207.38   $207.40   $207.40  
  Purchase #4 $17.70   10.517%   $19.5615   $19.56   $19.55   $19.60  
  Purchase #5 $68.58   11.356%   $76.3679   $76.37   $76.35   $76.40  
  Purchase #6 $93.59   6.146%   $99.342   $99.34   $99.35   $99.30  
  Purchase #7 $107.45   11.374%   $119.6714   $119.67   $119.65   $119.70  
  7 purchase totals = $790.69       $852.5128   $852.50   $852.50   $852.50