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 $53.37   10.376%   $58.9077   $58.91   $58.90   $58.90  
  Purchase #2 $33.53   11.274%   $37.3102   $37.31   $37.30   $37.30  
  Purchase #3 $233.93   12.209%   $262.4905   $262.49   $262.50   $262.50  
  Purchase #4 $248.47   3.811%   $257.9392   $257.94   $257.95   $257.90  
  Purchase #5 $147.29   8.687%   $160.0851   $160.09   $160.10   $160.10  
  Purchase #6 $249.50   13.546%   $283.2973   $283.30   $283.30   $283.30  
  Purchase #7 $185.36   9.857%   $203.6309   $203.63   $203.65   $203.60  
  7 purchase totals = $1,151.45       $1,263.6609   $1,263.67   $1,263.70   $1,263.60