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 $54.31   13.576%   $61.6831   $61.68   $61.70   $61.70  
  Purchase #2 $227.61   12.378%   $255.7836   $255.78   $255.80   $255.80  
  Purchase #3 $95.37   3.218%   $98.439   $98.44   $98.45   $98.40  
  Purchase #4 $223.40   11.362%   $248.7827   $248.78   $248.80   $248.80  
  Purchase #5 $161.90   5.735%   $171.185   $171.19   $171.20   $171.20  
  Purchase #6 $27.72   11.123%   $30.8033   $30.80   $30.80   $30.80  
  Purchase #7 $95.78   13.542%   $108.7505   $108.75   $108.75   $108.80  
  7 purchase totals = $886.09       $975.4272   $975.42   $975.50   $975.50