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 $119.26   13.500%   $135.3601   $135.36   $135.35   $135.40  
  Purchase #2 $220.68   9.496%   $241.6358   $241.64   $241.65   $241.60  
  Purchase #3 $116.95   8.580%   $126.9843   $126.98   $127.00   $127.00  
  Purchase #4 $177.89   8.624%   $193.2312   $193.23   $193.25   $193.20  
  Purchase #5 $226.57   6.502%   $241.3016   $241.30   $241.30   $241.30  
  Purchase #6 $138.49   3.487%   $143.3191   $143.32   $143.30   $143.30  
  Purchase #7 $112.48   3.537%   $116.4584   $116.46   $116.45   $116.50  
  7 purchase totals = $1,112.32       $1,198.2905   $1,198.29   $1,198.30   $1,198.30