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	$87.75	13.240%	$99.3681	$99.37	$99.35	$99.40
Purchase #2	$198.32	7.802%	$213.7929	$213.79	$213.80	$213.80
Purchase #3	$89.30	10.384%	$98.5729	$98.57	$98.55	$98.60
Purchase #4	$212.55	11.828%	$237.6904	$237.69	$237.70	$237.70
Purchase #5	$239.34	4.507%	$250.1271	$250.13	$250.15	$250.10
Purchase #6	$230.45	4.164%	$240.0459	$240.05	$240.05	$240.00
Purchase #7	$99.51	11.433%	$110.887	$110.89	$110.90	$110.90
7 purchase totals =	$1,157.22		$1,250.4843	$1,250.49	$1,250.50	$1,250.50