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 $95.85   6.341%   $101.9278   $101.93   $101.95   $101.90  
  Purchase #2 $108.35   8.676%   $117.7504   $117.75   $117.75   $117.80  
  Purchase #3 $74.92   12.357%   $84.1779   $84.18   $84.20   $84.20  
  Purchase #4 $173.55   11.726%   $193.9005   $193.90   $193.90   $193.90  
  Purchase #5 $87.37   4.753%   $91.5227   $91.52   $91.50   $91.50  
  Purchase #6 $168.44   8.245%   $182.3279   $182.33   $182.35   $182.30  
  Purchase #7 $246.73   13.620%   $280.3346   $280.33   $280.35   $280.30  
  7 purchase totals = $955.21       $1,051.9418   $1,051.94   $1,052.00   $1,051.90