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 $244.64   3.841%   $254.0366   $254.04   $254.05   $254.00  
  Purchase #2 $192.99   13.585%   $219.2077   $219.21   $219.20   $219.20  
  Purchase #3 $203.61   8.203%   $220.3121   $220.31   $220.30   $220.30  
  Purchase #4 $44.48   8.777%   $48.384   $48.38   $48.40   $48.40  
  Purchase #5 $193.40   4.121%   $201.37   $201.37   $201.35   $201.40  
  Purchase #6 $217.40   8.727%   $236.3725   $236.37   $236.35   $236.40  
  Purchase #7 $133.53   8.422%   $144.7759   $144.78   $144.80   $144.80  
  7 purchase totals = $1,230.05       $1,324.4588   $1,324.46   $1,324.45   $1,324.50