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	$234.96	3.868%	$244.0483	$244.05	$244.05	$244.00
Purchase #2	$33.74	4.638%	$35.3049	$35.30	$35.30	$35.30
Purchase #3	$240.54	6.391%	$255.9129	$255.91	$255.90	$255.90
Purchase #4	$179.25	4.105%	$186.6082	$186.61	$186.60	$186.60
Purchase #5	$72.44	12.592%	$81.5616	$81.56	$81.55	$81.60
Purchase #6	$125.93	4.345%	$131.4017	$131.40	$131.40	$131.40
Purchase #7	$37.71	13.164%	$42.6741	$42.67	$42.65	$42.70
7 purchase totals =	$924.57		$977.5117	$977.50	$977.45	$977.50