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 $42.59   12.121%   $47.7523   $47.75   $47.75   $47.80  
  Purchase #2 $147.38   4.154%   $153.5022   $153.50   $153.50   $153.50  
  Purchase #3 $208.74   4.146%   $217.3944   $217.39   $217.40   $217.40  
  Purchase #4 $223.29   3.614%   $231.3597   $231.36   $231.35   $231.40  
  Purchase #5 $223.56   12.397%   $251.2747   $251.27   $251.25   $251.30  
  Purchase #6 $196.40   10.106%   $216.2482   $216.25   $216.25   $216.20  
  Purchase #7 $66.69   9.446%   $72.9895   $72.99   $73.00   $73.00  
  7 purchase totals = $1,108.65       $1,190.5210   $1,190.51   $1,190.50   $1,190.60