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 $224.72   9.733%   $246.592   $246.59   $246.60   $246.60  
  Purchase #2 $236.29   11.128%   $262.5844   $262.58   $262.60   $262.60  
  Purchase #3 $123.77   4.808%   $129.7209   $129.72   $129.70   $129.70  
  Purchase #4 $166.33   6.374%   $176.9319   $176.93   $176.95   $176.90  
  Purchase #5 $88.82   9.789%   $97.5146   $97.51   $97.50   $97.50  
  Purchase #6 $102.77   7.224%   $110.1941   $110.19   $110.20   $110.20  
  Purchase #7 $150.48   9.144%   $164.2399   $164.24   $164.25   $164.20  
  7 purchase totals = $1,093.18       $1,187.7778   $1,187.76   $1,187.80   $1,187.70