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 $55.95   13.832%   $63.689   $63.69   $63.70   $63.70  
  Purchase #2 $240.39   13.118%   $271.9244   $271.92   $271.90   $271.90  
  Purchase #3 $95.80   9.301%   $104.7104   $104.71   $104.70   $104.70  
  Purchase #4 $176.42   13.482%   $200.2049   $200.20   $200.20   $200.20  
  Purchase #5 $171.85   10.536%   $189.9561   $189.96   $189.95   $190.00  
  Purchase #6 $68.39   11.231%   $76.0709   $76.07   $76.05   $76.10  
  Purchase #7 $113.71   6.158%   $120.7123   $120.71   $120.70   $120.70  
  7 purchase totals = $922.51       $1,027.2680   $1,027.26   $1,027.20   $1,027.30