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 $244.51   13.364%   $277.1863   $277.19   $277.20   $277.20  
  Purchase #2 $211.63   12.112%   $237.2626   $237.26   $237.25   $237.30  
  Purchase #3 $90.92   4.251%   $94.785   $94.79   $94.80   $94.80  
  Purchase #4 $219.98   12.839%   $248.2232   $248.22   $248.20   $248.20  
  Purchase #5 $240.86   12.551%   $271.0903   $271.09   $271.10   $271.10  
  Purchase #6 $221.54   13.752%   $252.0062   $252.01   $252.00   $252.00  
  Purchase #7 $85.38   9.762%   $93.7148   $93.71   $93.70   $93.70  
  7 purchase totals = $1,314.82       $1,474.2684   $1,474.27   $1,474.25   $1,474.30