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 $232.38   11.232%   $258.4809   $258.48   $258.50   $258.50  
  Purchase #2 $212.63   4.357%   $221.8943   $221.89   $221.90   $221.90  
  Purchase #3 $71.64   12.688%   $80.7297   $80.73   $80.75   $80.70  
  Purchase #4 $228.52   3.838%   $237.2906   $237.29   $237.30   $237.30  
  Purchase #5 $108.65   11.248%   $120.871   $120.87   $120.85   $120.90  
  Purchase #6 $14.81   12.646%   $16.6829   $16.68   $16.70   $16.70  
  Purchase #7 $22.61   6.840%   $24.1565   $24.16   $24.15   $24.20  
  7 purchase totals = $891.24       $960.1059   $960.10   $960.15   $960.20