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 $67.60   11.553%   $75.4098   $75.41   $75.40   $75.40  
  Purchase #2 $115.69   10.284%   $127.5876   $127.59   $127.60   $127.60  
  Purchase #3 $219.70   4.650%   $229.9161   $229.92   $229.90   $229.90  
  Purchase #4 $237.46   7.175%   $254.4978   $254.50   $254.50   $254.50  
  Purchase #5 $13.86   11.859%   $15.5037   $15.50   $15.50   $15.50  
  Purchase #6 $120.52   13.476%   $136.7613   $136.76   $136.75   $136.80  
  Purchase #7 $170.60   9.808%   $187.3324   $187.33   $187.35   $187.30  
  7 purchase totals = $945.43       $1,027.0087   $1,027.01   $1,027.00   $1,027.00