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 $91.51   5.311%   $96.3701   $96.37   $96.35   $96.40  
  Purchase #2 $101.48   11.800%   $113.4546   $113.45   $113.45   $113.50  
  Purchase #3 $183.56   10.429%   $202.7035   $202.70   $202.70   $202.70  
  Purchase #4 $15.97   4.395%   $16.6719   $16.67   $16.65   $16.70  
  Purchase #5 $73.83   6.376%   $78.5374   $78.54   $78.55   $78.50  
  Purchase #6 $26.50   8.370%   $28.7181   $28.72   $28.70   $28.70  
  Purchase #7 $181.68   13.843%   $206.83   $206.83   $206.85   $206.80  
  7 purchase totals = $674.53       $743.2856   $743.28   $743.25   $743.30