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 $56.28   6.493%   $59.9343   $59.93   $59.95   $59.90  
  Purchase #2 $192.81   10.302%   $212.6733   $212.67   $212.65   $212.70  
  Purchase #3 $249.53   8.185%   $269.954   $269.95   $269.95   $270.00  
  Purchase #4 $219.95   7.488%   $236.4199   $236.42   $236.40   $236.40  
  Purchase #5 $94.62   10.350%   $104.4132   $104.41   $104.40   $104.40  
  Purchase #6 $116.32   10.539%   $128.579   $128.58   $128.60   $128.60  
  Purchase #7 $56.86   8.324%   $61.593   $61.59   $61.60   $61.60  
  7 purchase totals = $986.37       $1,073.5667   $1,073.55   $1,073.55   $1,073.60