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 $69.81   9.767%   $76.6283   $76.63   $76.65   $76.60  
  Purchase #2 $155.79   13.429%   $176.711   $176.71   $176.70   $176.70  
  Purchase #3 $184.37   11.703%   $205.9468   $205.95   $205.95   $205.90  
  Purchase #4 $24.53   11.805%   $27.4258   $27.43   $27.45   $27.40  
  Purchase #5 $79.30   11.363%   $88.3109   $88.31   $88.30   $88.30  
  Purchase #6 $25.48   5.463%   $26.872   $26.87   $26.85   $26.90  
  Purchase #7 $116.84   10.776%   $129.4307   $129.43   $129.45   $129.40  
  7 purchase totals = $656.12       $731.3255   $731.33   $731.35   $731.20