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 $201.88   3.282%   $208.5057   $208.51   $208.50   $208.50  
  Purchase #2 $29.77   13.312%   $33.733   $33.73   $33.75   $33.70  
  Purchase #3 $214.31   5.568%   $226.2428   $226.24   $226.25   $226.20  
  Purchase #4 $76.65   4.147%   $79.8287   $79.83   $79.85   $79.80  
  Purchase #5 $108.48   11.433%   $120.8825   $120.88   $120.90   $120.90  
  Purchase #6 $81.52   3.814%   $84.6292   $84.63   $84.65   $84.60  
  Purchase #7 $120.49   11.738%   $134.6331   $134.63   $134.65   $134.60  
  7 purchase totals = $833.10       $888.4550   $888.45   $888.55   $888.30