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 $215.38   13.663%   $244.8074   $244.81   $244.80   $244.80  
  Purchase #2 $121.48   10.507%   $134.2439   $134.24   $134.25   $134.20  
  Purchase #3 $210.35   3.461%   $217.6302   $217.63   $217.65   $217.60  
  Purchase #4 $8.45   7.753%   $9.1051   $9.11   $9.10   $9.10  
  Purchase #5 $114.31   6.337%   $121.5538   $121.55   $121.55   $121.60  
  Purchase #6 $39.28   13.392%   $44.5404   $44.54   $44.55   $44.50  
  Purchase #7 $208.78   12.365%   $234.5956   $234.60   $234.60   $234.60  
  7 purchase totals = $918.03       $1,006.4764   $1,006.48   $1,006.50   $1,006.40