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 $89.90   6.752%   $95.97   $95.97   $95.95   $96.00  
  Purchase #2 $63.62   5.324%   $67.0071   $67.01   $67.00   $67.00  
  Purchase #3 $65.94   7.475%   $70.869   $70.87   $70.85   $70.90  
  Purchase #4 $177.80   3.800%   $184.5564   $184.56   $184.55   $184.60  
  Purchase #5 $35.95   8.626%   $39.051   $39.05   $39.05   $39.10  
  Purchase #6 $98.82   6.652%   $105.3935   $105.39   $105.40   $105.40  
  Purchase #7 $183.28   13.274%   $207.6086   $207.61   $207.60   $207.60  
  7 purchase totals = $715.31       $770.4556   $770.46   $770.40   $770.60