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 $44.30   7.510%   $47.6269   $47.63   $47.65   $47.60  
  Purchase #2 $83.52   11.492%   $93.1181   $93.12   $93.10   $93.10  
  Purchase #3 $15.54   3.734%   $16.1203   $16.12   $16.10   $16.10  
  Purchase #4 $117.44   13.615%   $133.4295   $133.43   $133.45   $133.40  
  Purchase #5 $114.53   8.737%   $124.5365   $124.54   $124.55   $124.50  
  Purchase #6 $235.43   4.288%   $245.5252   $245.53   $245.55   $245.50  
  Purchase #7 $56.90   13.366%   $64.5053   $64.51   $64.50   $64.50  
  7 purchase totals = $667.66       $724.8618   $724.88   $724.90   $724.70