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 $62.82   12.266%   $70.5255   $70.53   $70.55   $70.50  
  Purchase #2 $40.54   4.417%   $42.3307   $42.33   $42.35   $42.30  
  Purchase #3 $142.52   3.125%   $146.9738   $146.97   $146.95   $147.00  
  Purchase #4 $71.74   6.230%   $76.2094   $76.21   $76.20   $76.20  
  Purchase #5 $241.71   13.245%   $273.7245   $273.72   $273.70   $273.70  
  Purchase #6 $49.91   8.111%   $53.9582   $53.96   $53.95   $54.00  
  Purchase #7 $231.76   12.517%   $260.7694   $260.77   $260.75   $260.80  
  7 purchase totals = $841.00       $924.4915   $924.49   $924.45   $924.50