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 $32.93   13.365%   $37.3311   $37.33   $37.35   $37.30  
  Purchase #2 $62.91   12.587%   $70.8285   $70.83   $70.85   $70.80  
  Purchase #3 $215.93   4.167%   $224.9278   $224.93   $224.95   $224.90  
  Purchase #4 $197.56   7.416%   $212.211   $212.21   $212.20   $212.20  
  Purchase #5 $87.67   10.592%   $96.956   $96.96   $96.95   $97.00  
  Purchase #6 $57.45   8.834%   $62.5251   $62.53   $62.55   $62.50  
  Purchase #7 $231.55   6.804%   $247.3047   $247.30   $247.30   $247.30  
  7 purchase totals = $886.00       $952.0842   $952.09   $952.15   $952.00