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	$124.71	11.841%	$139.4769	$139.48	$139.50	$139.50
Purchase #2	$234.46	8.675%	$254.7994	$254.80	$254.80	$254.80
Purchase #3	$30.30	11.864%	$33.8948	$33.89	$33.90	$33.90
Purchase #4	$35.59	8.316%	$38.5497	$38.55	$38.55	$38.50
Purchase #5	$110.46	3.333%	$114.1416	$114.14	$114.15	$114.10
Purchase #6	$211.67	13.659%	$240.582	$240.58	$240.60	$240.60
Purchase #7	$97.28	8.768%	$105.8095	$105.81	$105.80	$105.80
7 purchase totals =	$844.47		$927.2539	$927.25	$927.30	$927.20