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 $82.47   12.766%   $92.9981   $93.00   $93.00   $93.00  
  Purchase #2 $192.87   4.506%   $201.5607   $201.56   $201.55   $201.60  
  Purchase #3 $227.58   4.471%   $237.7551   $237.76   $237.75   $237.80  
  Purchase #4 $32.57   8.551%   $35.3551   $35.36   $35.35   $35.40  
  Purchase #5 $135.29   4.852%   $141.8543   $141.85   $141.85   $141.90  
  Purchase #6 $79.75   12.622%   $89.816   $89.82   $89.80   $89.80  
  Purchase #7 $14.96   12.274%   $16.7962   $16.80   $16.80   $16.80  
  7 purchase totals = $765.49       $816.1355   $816.15   $816.10   $816.30