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 $204.88   13.710%   $232.969   $232.97   $232.95   $233.00  
  Purchase #2 $229.43   3.217%   $236.8108   $236.81   $236.80   $236.80  
  Purchase #3 $52.97   8.523%   $57.4846   $57.48   $57.50   $57.50  
  Purchase #4 $36.47   8.392%   $39.5306   $39.53   $39.55   $39.50  
  Purchase #5 $54.82   8.586%   $59.5268   $59.53   $59.55   $59.50  
  Purchase #6 $104.49   5.615%   $110.3571   $110.36   $110.35   $110.40  
  Purchase #7 $248.73   10.512%   $274.8765   $274.88   $274.90   $274.90  
  7 purchase totals = $931.79       $1,011.5554   $1,011.56   $1,011.60   $1,011.60