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 $37.61   9.658%   $41.2424   $41.24   $41.25   $41.20  
  Purchase #2 $112.87   7.738%   $121.6039   $121.60   $121.60   $121.60  
  Purchase #3 $177.34   9.226%   $193.7014   $193.70   $193.70   $193.70  
  Purchase #4 $88.42   10.104%   $97.354   $97.35   $97.35   $97.40  
  Purchase #5 $201.44   11.357%   $224.3175   $224.32   $224.30   $224.30  
  Purchase #6 $248.57   11.312%   $276.6882   $276.69   $276.70   $276.70  
  Purchase #7 $216.30   12.487%   $243.3094   $243.31   $243.30   $243.30  
  7 purchase totals = $1,082.55       $1,198.2168   $1,198.21   $1,198.20   $1,198.20