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 $232.33   6.718%   $247.9379   $247.94   $247.95   $247.90  
  Purchase #2 $174.48   8.439%   $189.2044   $189.20   $189.20   $189.20  
  Purchase #3 $169.58   4.743%   $177.6232   $177.62   $177.60   $177.60  
  Purchase #4 $206.34   4.785%   $216.2134   $216.21   $216.20   $216.20  
  Purchase #5 $62.81   3.452%   $64.9782   $64.98   $65.00   $65.00  
  Purchase #6 $235.25   8.872%   $256.1214   $256.12   $256.10   $256.10  
  Purchase #7 $38.97   8.246%   $42.1835   $42.18   $42.20   $42.20  
  7 purchase totals = $1,119.76       $1,194.2620   $1,194.25   $1,194.25   $1,194.20