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 $173.75   4.102%   $180.8772   $180.88   $180.90   $180.90  
  Purchase #2 $136.35   8.782%   $148.3243   $148.32   $148.30   $148.30  
  Purchase #3 $140.39   6.400%   $149.375   $149.38   $149.40   $149.40  
  Purchase #4 $10.91   10.392%   $12.0438   $12.04   $12.05   $12.00  
  Purchase #5 $42.46   4.654%   $44.4361   $44.44   $44.45   $44.40  
  Purchase #6 $93.61   6.844%   $100.0167   $100.02   $100.00   $100.00  
  Purchase #7 $228.31   3.765%   $236.9059   $236.91   $236.90   $236.90  
  7 purchase totals = $825.78       $871.9790   $871.99   $872.00   $871.90