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	$239.50	6.401%	$254.8304	$254.83	$254.85	$254.80
Purchase #2	$32.34	12.170%	$36.2758	$36.28	$36.30	$36.30
Purchase #3	$241.82	3.504%	$250.2934	$250.29	$250.30	$250.30
Purchase #4	$53.80	11.191%	$59.8208	$59.82	$59.80	$59.80
Purchase #5	$46.70	7.624%	$50.2604	$50.26	$50.25	$50.30
Purchase #6	$34.69	9.427%	$37.9602	$37.96	$37.95	$38.00
Purchase #7	$130.49	8.121%	$141.0871	$141.09	$141.10	$141.10
7 purchase totals =	$779.34		$830.5281	$830.53	$830.55	$830.60