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 $186.99   12.819%   $210.9602   $210.96   $210.95   $211.00  
  Purchase #2 $80.92   10.110%   $89.101   $89.10   $89.10   $89.10  
  Purchase #3 $22.41   10.355%   $24.7306   $24.73   $24.75   $24.70  
  Purchase #4 $205.56   4.722%   $215.2665   $215.27   $215.25   $215.30  
  Purchase #5 $141.96   12.652%   $159.9208   $159.92   $159.90   $159.90  
  Purchase #6 $236.39   5.379%   $249.1054   $249.11   $249.10   $249.10  
  Purchase #7 $167.70   8.193%   $181.4397   $181.44   $181.45   $181.40  
  7 purchase totals = $1,041.93       $1,130.5242   $1,130.53   $1,130.50   $1,130.50