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 $246.93   13.437%   $280.11   $280.11   $280.10   $280.10  
  Purchase #2 $96.87   5.369%   $102.071   $102.07   $102.05   $102.10  
  Purchase #3 $168.31   7.276%   $180.5562   $180.56   $180.55   $180.60  
  Purchase #4 $213.79   10.847%   $236.9798   $236.98   $237.00   $237.00  
  Purchase #5 $196.51   10.501%   $217.1455   $217.15   $217.15   $217.10  
  Purchase #6 $192.94   12.234%   $216.5443   $216.54   $216.55   $216.50  
  Purchase #7 $212.74   9.213%   $232.3397   $232.34   $232.35   $232.30  
  7 purchase totals = $1,328.09       $1,465.7465   $1,465.75   $1,465.75   $1,465.70