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 $161.89   13.735%   $184.1256   $184.13   $184.15   $184.10  
  Purchase #2 $173.41   11.467%   $193.2949   $193.29   $193.30   $193.30  
  Purchase #3 $149.86   6.522%   $159.6339   $159.63   $159.65   $159.60  
  Purchase #4 $53.80   13.791%   $61.2196   $61.22   $61.20   $61.20  
  Purchase #5 $42.47   8.377%   $46.0277   $46.03   $46.05   $46.00  
  Purchase #6 $169.42   5.316%   $178.4264   $178.43   $178.45   $178.40  
  Purchase #7 $178.44   12.525%   $200.7896   $200.79   $200.80   $200.80  
  7 purchase totals = $929.29       $1,023.5177   $1,023.52   $1,023.60   $1,023.40