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 $234.30   8.291%   $253.7258   $253.73   $253.75   $253.70  
  Purchase #2 $164.87   4.710%   $172.6354   $172.64   $172.65   $172.60  
  Purchase #3 $9.91   4.537%   $10.3596   $10.36   $10.35   $10.40  
  Purchase #4 $167.79   6.752%   $179.1192   $179.12   $179.10   $179.10  
  Purchase #5 $99.85   8.186%   $108.0237   $108.02   $108.00   $108.00  
  Purchase #6 $237.42   4.823%   $248.8708   $248.87   $248.85   $248.90  
  Purchase #7 $193.61   6.306%   $205.819   $205.82   $205.80   $205.80  
  7 purchase totals = $1,107.75       $1,178.5535   $1,178.56   $1,178.50   $1,178.50