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 $59.84   10.166%   $65.9233   $65.92   $65.90   $65.90  
  Purchase #2 $240.34   7.301%   $257.8872   $257.89   $257.90   $257.90  
  Purchase #3 $44.72   8.142%   $48.3611   $48.36   $48.35   $48.40  
  Purchase #4 $226.90   10.108%   $249.8351   $249.84   $249.85   $249.80  
  Purchase #5 $207.29   3.792%   $215.1504   $215.15   $215.15   $215.20  
  Purchase #6 $157.80   3.112%   $162.7107   $162.71   $162.70   $162.70  
  Purchase #7 $13.46   6.248%   $14.301   $14.30   $14.30   $14.30  
  7 purchase totals = $950.35       $1,014.1688   $1,014.17   $1,014.15   $1,014.20