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 $241.58   7.230%   $259.0462   $259.05   $259.05   $259.00  
  Purchase #2 $224.51   10.694%   $248.5191   $248.52   $248.50   $248.50  
  Purchase #3 $91.41   4.706%   $95.7118   $95.71   $95.70   $95.70  
  Purchase #4 $21.45   13.234%   $24.2887   $24.29   $24.30   $24.30  
  Purchase #5 $229.43   9.386%   $250.9643   $250.96   $250.95   $251.00  
  Purchase #6 $114.34   10.240%   $126.0484   $126.05   $126.05   $126.00  
  Purchase #7 $25.70   12.297%   $28.8603   $28.86   $28.85   $28.90  
  7 purchase totals = $948.42       $1,033.4388   $1,033.44   $1,033.40   $1,033.40