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 $71.48   3.234%   $73.7917   $73.79   $73.80   $73.80  
  Purchase #2 $170.99   9.331%   $186.9451   $186.95   $186.95   $186.90  
  Purchase #3 $57.95   11.454%   $64.5876   $64.59   $64.60   $64.60  
  Purchase #4 $43.41   8.812%   $47.2353   $47.24   $47.25   $47.20  
  Purchase #5 $151.93   13.176%   $171.9483   $171.95   $171.95   $171.90  
  Purchase #6 $219.89   13.217%   $248.9529   $248.95   $248.95   $249.00  
  Purchase #7 $221.48   8.776%   $240.9171   $240.92   $240.90   $240.90  
  7 purchase totals = $937.13       $1,034.3780   $1,034.39   $1,034.40   $1,034.30