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	$45.59	9.817%	$50.0656	$50.07	$50.05	$50.10
Purchase #2	$116.79	8.850%	$127.1259	$127.13	$127.15	$127.10
Purchase #3	$127.71	4.415%	$133.3484	$133.35	$133.35	$133.30
Purchase #4	$80.56	11.632%	$89.9307	$89.93	$89.95	$89.90
Purchase #5	$67.75	9.114%	$73.9247	$73.92	$73.90	$73.90
Purchase #6	$219.89	10.723%	$243.4688	$243.47	$243.45	$243.50
Purchase #7	$71.26	8.340%	$77.2031	$77.20	$77.20	$77.20
7 purchase totals =	$729.55		$795.0672	$795.07	$795.05	$795.00