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 $66.95   5.467%   $70.6102   $70.61   $70.60   $70.60  
  Purchase #2 $212.28   11.316%   $236.3016   $236.30   $236.30   $236.30  
  Purchase #3 $243.82   13.554%   $276.8674   $276.87   $276.85   $276.90  
  Purchase #4 $208.27   7.530%   $223.9527   $223.95   $223.95   $224.00  
  Purchase #5 $250.47   12.819%   $282.5777   $282.58   $282.60   $282.60  
  Purchase #6 $98.36   12.323%   $110.4809   $110.48   $110.50   $110.50  
  Purchase #7 $150.57   10.454%   $166.3106   $166.31   $166.30   $166.30  
  7 purchase totals = $1,230.72       $1,367.1011   $1,367.10   $1,367.10   $1,367.20