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 $227.42   9.836%   $249.789   $249.79   $249.80   $249.80  
  Purchase #2 $181.36   13.228%   $205.3503   $205.35   $205.35   $205.40  
  Purchase #3 $20.60   8.453%   $22.3413   $22.34   $22.35   $22.30  
  Purchase #4 $98.65   9.740%   $108.2585   $108.26   $108.25   $108.30  
  Purchase #5 $32.93   5.264%   $34.6634   $34.66   $34.65   $34.70  
  Purchase #6 $245.58   8.336%   $266.0515   $266.05   $266.05   $266.10  
  Purchase #7 $214.77   12.661%   $241.962   $241.96   $241.95   $242.00  
  7 purchase totals = $1,021.31       $1,128.4160   $1,128.41   $1,128.40   $1,128.60