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 $131.62   7.226%   $141.1309   $141.13   $141.15   $141.10  
  Purchase #2 $168.66   4.463%   $176.1873   $176.19   $176.20   $176.20  
  Purchase #3 $44.91   5.368%   $47.3208   $47.32   $47.30   $47.30  
  Purchase #4 $218.31   8.295%   $236.4188   $236.42   $236.40   $236.40  
  Purchase #5 $43.40   7.471%   $46.6424   $46.64   $46.65   $46.60  
  Purchase #6 $115.26   5.676%   $121.8022   $121.80   $121.80   $121.80  
  Purchase #7 $213.49   7.287%   $229.047   $229.05   $229.05   $229.00  
  7 purchase totals = $935.65       $998.5494   $998.55   $998.55   $998.40