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 $192.56   11.331%   $214.379   $214.38   $214.40   $214.40  
  Purchase #2 $103.84   8.195%   $112.3497   $112.35   $112.35   $112.30  
  Purchase #3 $60.58   5.720%   $64.0452   $64.05   $64.05   $64.00  
  Purchase #4 $198.92   13.383%   $225.5415   $225.54   $225.55   $225.50  
  Purchase #5 $39.29   12.587%   $44.2354   $44.24   $44.25   $44.20  
  Purchase #6 $59.70   5.119%   $62.756   $62.76   $62.75   $62.80  
  Purchase #7 $126.38   4.190%   $131.6753   $131.68   $131.70   $131.70  
  7 purchase totals = $781.27       $854.9821   $855.00   $855.05   $854.90