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 $176.31   10.137%   $194.1825   $194.18   $194.20   $194.20  
  Purchase #2 $146.34   4.123%   $152.3736   $152.37   $152.35   $152.40  
  Purchase #3 $138.67   7.506%   $149.0786   $149.08   $149.10   $149.10  
  Purchase #4 $161.55   8.869%   $175.8779   $175.88   $175.90   $175.90  
  Purchase #5 $213.95   10.409%   $236.2201   $236.22   $236.20   $236.20  
  Purchase #6 $209.38   11.231%   $232.8955   $232.90   $232.90   $232.90  
  Purchase #7 $146.56   13.231%   $165.9514   $165.95   $165.95   $166.00  
  7 purchase totals = $1,192.76       $1,306.5796   $1,306.58   $1,306.60   $1,306.70