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 $229.61   7.559%   $246.9662   $246.97   $246.95   $247.00  
  Purchase #2 $117.87   5.489%   $124.3399   $124.34   $124.35   $124.30  
  Purchase #3 $61.51   12.596%   $69.2578   $69.26   $69.25   $69.30  
  Purchase #4 $162.47   13.867%   $184.9997   $185.00   $185.00   $185.00  
  Purchase #5 $40.60   9.532%   $44.47   $44.47   $44.45   $44.50  
  Purchase #6 $171.97   11.230%   $191.2822   $191.28   $191.30   $191.30  
  Purchase #7 $146.85   4.687%   $153.7329   $153.73   $153.75   $153.70  
  7 purchase totals = $930.88       $1,015.0487   $1,015.05   $1,015.05   $1,015.10