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 $207.67   10.289%   $229.0372   $229.04   $229.05   $229.00  
  Purchase #2 $56.63   7.680%   $60.9792   $60.98   $61.00   $61.00  
  Purchase #3 $154.85   4.336%   $161.5643   $161.56   $161.55   $161.60  
  Purchase #4 $206.57   6.226%   $219.431   $219.43   $219.45   $219.40  
  Purchase #5 $132.96   8.866%   $144.7482   $144.75   $144.75   $144.70  
  Purchase #6 $108.74   4.394%   $113.518   $113.52   $113.50   $113.50  
  Purchase #7 $85.81   10.723%   $95.0114   $95.01   $95.00   $95.00  
  7 purchase totals = $953.23       $1,024.2893   $1,024.29   $1,024.30   $1,024.20