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 $86.28   12.160%   $96.7716   $96.77   $96.75   $96.80  
  Purchase #2 $204.95   4.412%   $213.9924   $213.99   $214.00   $214.00  
  Purchase #3 $221.47   7.394%   $237.8455   $237.85   $237.85   $237.80  
  Purchase #4 $75.59   11.837%   $84.5376   $84.54   $84.55   $84.50  
  Purchase #5 $61.91   10.378%   $68.335   $68.34   $68.35   $68.30  
  Purchase #6 $185.43   9.305%   $202.6843   $202.68   $202.70   $202.70  
  Purchase #7 $109.45   3.774%   $113.5806   $113.58   $113.60   $113.60  
  7 purchase totals = $945.08       $1,017.7470   $1,017.75   $1,017.80   $1,017.70