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 $217.68   5.778%   $230.2576   $230.26   $230.25   $230.30  
  Purchase #2 $97.63   13.274%   $110.5894   $110.59   $110.60   $110.60  
  Purchase #3 $154.43   10.306%   $170.3456   $170.35   $170.35   $170.30  
  Purchase #4 $121.33   12.800%   $136.8602   $136.86   $136.85   $136.90  
  Purchase #5 $157.97   8.579%   $171.5222   $171.52   $171.50   $171.50  
  Purchase #6 $139.27   12.861%   $157.1815   $157.18   $157.20   $157.20  
  Purchase #7 $79.91   4.329%   $83.3693   $83.37   $83.35   $83.40  
  7 purchase totals = $968.22       $1,060.1258   $1,060.13   $1,060.10   $1,060.20