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 $54.34   7.632%   $58.4872   $58.49   $58.50   $58.50  
  Purchase #2 $129.59   3.837%   $134.5624   $134.56   $134.55   $134.60  
  Purchase #3 $147.33   11.683%   $164.5426   $164.54   $164.55   $164.50  
  Purchase #4 $92.63   10.740%   $102.5785   $102.58   $102.60   $102.60  
  Purchase #5 $226.66   3.465%   $234.5138   $234.51   $234.50   $234.50  
  Purchase #6 $57.47   5.774%   $60.7883   $60.79   $60.80   $60.80  
  Purchase #7 $245.63   10.217%   $270.726   $270.73   $270.75   $270.70  
  7 purchase totals = $953.65       $1,026.1988   $1,026.20   $1,026.25   $1,026.20