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 $238.72   13.676%   $271.3673   $271.37   $271.35   $271.40  
  Purchase #2 $39.93   13.825%   $45.4503   $45.45   $45.45   $45.50  
  Purchase #3 $223.75   5.549%   $236.1659   $236.17   $236.15   $236.20  
  Purchase #4 $86.47   6.406%   $92.0093   $92.01   $92.00   $92.00  
  Purchase #5 $81.79   10.826%   $90.6446   $90.64   $90.65   $90.60  
  Purchase #6 $11.25   5.740%   $11.8958   $11.90   $11.90   $11.90  
  Purchase #7 $249.99   6.797%   $266.9818   $266.98   $267.00   $267.00  
  7 purchase totals = $931.90       $1,014.5150   $1,014.52   $1,014.50   $1,014.60