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	$80.33	11.492%	$89.5615	$89.56	$89.55	$89.60
Purchase #2	$66.68	3.774%	$69.1965	$69.20	$69.20	$69.20
Purchase #3	$53.31	8.363%	$57.7683	$57.77	$57.75	$57.80
Purchase #4	$6.47	11.405%	$7.2079	$7.21	$7.20	$7.20
Purchase #5	$30.92	4.206%	$32.2205	$32.22	$32.20	$32.20
Purchase #6	$56.29	9.274%	$61.5103	$61.51	$61.50	$61.50
Purchase #7	$34.89	7.635%	$37.5539	$37.55	$37.55	$37.60
7 purchase totals =	$328.89		$355.0189	$355.02	$354.95	$355.10