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	$120.69	7.168%	$129.3411	$129.34	$129.35	$129.30
Purchase #2	$57.84	7.389%	$62.1138	$62.11	$62.10	$62.10
Purchase #3	$146.82	7.787%	$158.2529	$158.25	$158.25	$158.30
Purchase #4	$138.26	4.446%	$144.407	$144.41	$144.40	$144.40
Purchase #5	$78.41	11.172%	$87.17	$87.17	$87.15	$87.20
Purchase #6	$226.71	7.499%	$243.711	$243.71	$243.70	$243.70
Purchase #7	$80.57	11.142%	$89.5471	$89.55	$89.55	$89.50
7 purchase totals =	$849.30		$914.5429	$914.54	$914.50	$914.50