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 $65.99   13.773%   $75.0788   $75.08   $75.10   $75.10  
  Purchase #2 $167.39   4.867%   $175.5369   $175.54   $175.55   $175.50  
  Purchase #3 $76.55   13.610%   $86.9685   $86.97   $86.95   $87.00  
  Purchase #4 $159.38   8.711%   $173.2636   $173.26   $173.25   $173.30  
  Purchase #5 $216.83   10.288%   $239.1375   $239.14   $239.15   $239.10  
  Purchase #6 $160.68   13.689%   $182.6755   $182.68   $182.70   $182.70  
  Purchase #7 $75.89   11.122%   $84.3305   $84.33   $84.35   $84.30  
  7 purchase totals = $922.71       $1,016.9913   $1,017.00   $1,017.05   $1,017.00