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 $136.58   10.809%   $151.3429   $151.34   $151.35   $151.30  
  Purchase #2 $170.58   12.516%   $191.9298   $191.93   $191.95   $191.90  
  Purchase #3 $25.95   6.737%   $27.6983   $27.70   $27.70   $27.70  
  Purchase #4 $14.82   6.198%   $15.7385   $15.74   $15.75   $15.70  
  Purchase #5 $16.79   12.171%   $18.8335   $18.83   $18.85   $18.80  
  Purchase #6 $141.47   11.123%   $157.2057   $157.21   $157.20   $157.20  
  Purchase #7 $191.46   7.593%   $205.9976   $206.00   $206.00   $206.00  
  7 purchase totals = $697.65       $768.7463   $768.75   $768.80   $768.60