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 $82.95   13.382%   $94.0504   $94.05   $94.05   $94.10  
  Purchase #2 $241.71   3.580%   $250.3632   $250.36   $250.35   $250.40  
  Purchase #3 $12.98   3.199%   $13.3952   $13.40   $13.40   $13.40  
  Purchase #4 $181.69   13.404%   $206.0437   $206.04   $206.05   $206.00  
  Purchase #5 $105.41   13.566%   $119.7099   $119.71   $119.70   $119.70  
  Purchase #6 $165.97   3.754%   $172.2005   $172.20   $172.20   $172.20  
  Purchase #7 $126.78   8.355%   $137.3725   $137.37   $137.35   $137.40  
  7 purchase totals = $917.49       $993.1354   $993.13   $993.10   $993.20