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	$99.79	9.355%	$109.1254	$109.13	$109.15	$109.10
Purchase #2	$58.99	11.403%	$65.7166	$65.72	$65.70	$65.70
Purchase #3	$129.74	12.582%	$146.0639	$146.06	$146.05	$146.10
Purchase #4	$197.69	7.561%	$212.6373	$212.64	$212.65	$212.60
Purchase #5	$88.59	4.105%	$92.2266	$92.23	$92.25	$92.20
Purchase #6	$240.53	5.696%	$254.2306	$254.23	$254.25	$254.20
Purchase #7	$85.98	3.765%	$89.2171	$89.22	$89.20	$89.20
7 purchase totals =	$901.31		$969.2175	$969.23	$969.25	$969.10