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 $48.38   13.860%   $55.0855   $55.09   $55.10   $55.10  
  Purchase #2 $173.32   11.853%   $193.8636   $193.86   $193.85   $193.90  
  Purchase #3 $75.28   12.228%   $84.4852   $84.49   $84.50   $84.50  
  Purchase #4 $243.92   8.449%   $264.5288   $264.53   $264.55   $264.50  
  Purchase #5 $114.25   8.798%   $124.3017   $124.30   $124.30   $124.30  
  Purchase #6 $243.82   3.621%   $252.6487   $252.65   $252.65   $252.60  
  Purchase #7 $212.42   4.541%   $222.066   $222.07   $222.05   $222.10  
  7 purchase totals = $1,111.39       $1,196.9795   $1,196.99   $1,197.00   $1,197.00