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 $249.73   6.502%   $265.9674   $265.97   $265.95   $266.00  
  Purchase #2 $30.59   10.162%   $33.6986   $33.70   $33.70   $33.70  
  Purchase #3 $57.76   4.286%   $60.2356   $60.24   $60.25   $60.20  
  Purchase #4 $176.65   9.834%   $194.0218   $194.02   $194.00   $194.00  
  Purchase #5 $11.35   6.800%   $12.1218   $12.12   $12.10   $12.10  
  Purchase #6 $70.77   7.117%   $75.8067   $75.81   $75.80   $75.80  
  Purchase #7 $102.40   11.765%   $114.4474   $114.45   $114.45   $114.40  
  7 purchase totals = $699.25       $756.2993   $756.31   $756.25   $756.20