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 $205.34   13.837%   $233.7529   $233.75   $233.75   $233.80  
  Purchase #2 $26.40   10.163%   $29.083   $29.08   $29.10   $29.10  
  Purchase #3 $110.73   7.117%   $118.6107   $118.61   $118.60   $118.60  
  Purchase #4 $69.96   6.211%   $74.3052   $74.31   $74.30   $74.30  
  Purchase #5 $25.31   11.831%   $28.3044   $28.30   $28.30   $28.30  
  Purchase #6 $222.97   5.757%   $235.8064   $235.81   $235.80   $235.80  
  Purchase #7 $52.66   3.136%   $54.3114   $54.31   $54.30   $54.30  
  7 purchase totals = $713.37       $774.1740   $774.17   $774.15   $774.20