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 $111.86   11.271%   $124.4677   $124.47   $124.45   $124.50  
  Purchase #2 $173.63   3.790%   $180.2106   $180.21   $180.20   $180.20  
  Purchase #3 $208.44   13.647%   $236.8858   $236.89   $236.90   $236.90  
  Purchase #4 $98.61   10.561%   $109.0242   $109.02   $109.00   $109.00  
  Purchase #5 $155.69   3.812%   $161.6249   $161.62   $161.60   $161.60  
  Purchase #6 $152.62   8.339%   $165.347   $165.35   $165.35   $165.30  
  Purchase #7 $59.42   10.754%   $65.81   $65.81   $65.80   $65.80  
  7 purchase totals = $960.27       $1,043.3702   $1,043.37   $1,043.30   $1,043.30