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 $92.98   4.132%   $96.8219   $96.82   $96.80   $96.80  
  Purchase #2 $101.70   7.378%   $109.2034   $109.20   $109.20   $109.20  
  Purchase #3 $154.37   13.294%   $174.8919   $174.89   $174.90   $174.90  
  Purchase #4 $52.45   11.266%   $58.359   $58.36   $58.35   $58.40  
  Purchase #5 $203.94   3.164%   $210.3927   $210.39   $210.40   $210.40  
  Purchase #6 $168.40   11.654%   $188.0253   $188.03   $188.05   $188.00  
  Purchase #7 $21.59   7.170%   $23.138   $23.14   $23.15   $23.10  
  7 purchase totals = $795.43       $860.8322   $860.83   $860.85   $860.80