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	$81.63	9.356%	$89.2673	$89.27	$89.25	$89.30
Purchase #2	$51.70	7.180%	$55.4121	$55.41	$55.40	$55.40
Purchase #3	$155.67	9.775%	$170.8867	$170.89	$170.90	$170.90
Purchase #4	$187.38	13.559%	$212.7869	$212.79	$212.80	$212.80
Purchase #5	$198.27	11.843%	$221.7511	$221.75	$221.75	$221.80
Purchase #6	$192.81	12.796%	$217.482	$217.48	$217.50	$217.50
Purchase #7	$35.93	3.681%	$37.2526	$37.25	$37.25	$37.30
7 purchase totals =	$903.39		$1,004.8387	$1,004.84	$1,004.85	$1,005.00