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 $103.66   12.533%   $116.6517   $116.65   $116.65   $116.70  
  Purchase #2 $90.27   13.501%   $102.4574   $102.46   $102.45   $102.50  
  Purchase #3 $210.63   10.135%   $231.9774   $231.98   $232.00   $232.00  
  Purchase #4 $76.59   7.804%   $82.5671   $82.57   $82.55   $82.60  
  Purchase #5 $209.78   5.130%   $220.5417   $220.54   $220.55   $220.50  
  Purchase #6 $134.96   12.433%   $151.7396   $151.74   $151.75   $151.70  
  Purchase #7 $111.31   7.236%   $119.3644   $119.36   $119.35   $119.40  
  7 purchase totals = $937.20       $1,025.2993   $1,025.30   $1,025.30   $1,025.40