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 $104.97   11.791%   $117.347   $117.35   $117.35   $117.30  
  Purchase #2 $51.42   8.773%   $55.9311   $55.93   $55.95   $55.90  
  Purchase #3 $74.48   10.733%   $82.4739   $82.47   $82.45   $82.50  
  Purchase #4 $99.50   8.442%   $107.8998   $107.90   $107.90   $107.90  
  Purchase #5 $247.78   9.456%   $271.2101   $271.21   $271.20   $271.20  
  Purchase #6 $203.34   4.821%   $213.143   $213.14   $213.15   $213.10  
  Purchase #7 $167.31   9.438%   $183.1007   $183.10   $183.10   $183.10  
  7 purchase totals = $948.80       $1,031.1056   $1,031.10   $1,031.10   $1,031.00