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 $67.67   6.659%   $72.1761   $72.18   $72.20   $72.20  
  Purchase #2 $167.71   9.766%   $184.0886   $184.09   $184.10   $184.10  
  Purchase #3 $247.77   11.742%   $276.8632   $276.86   $276.85   $276.90  
  Purchase #4 $6.32   5.697%   $6.6801   $6.68   $6.70   $6.70  
  Purchase #5 $85.46   9.754%   $93.7958   $93.80   $93.80   $93.80  
  Purchase #6 $153.93   12.274%   $172.8234   $172.82   $172.80   $172.80  
  Purchase #7 $79.48   13.312%   $90.0604   $90.06   $90.05   $90.10  
  7 purchase totals = $808.34       $896.4876   $896.49   $896.50   $896.60