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	$61.76	13.529%	$70.1155	$70.12	$70.10	$70.10
Purchase #2	$78.69	5.350%	$82.8999	$82.90	$82.90	$82.90
Purchase #3	$82.64	11.589%	$92.2171	$92.22	$92.20	$92.20
Purchase #4	$70.31	3.559%	$72.8123	$72.81	$72.80	$72.80
Purchase #5	$195.76	7.352%	$210.1523	$210.15	$210.15	$210.20
Purchase #6	$64.84	11.306%	$72.1708	$72.17	$72.15	$72.20
Purchase #7	$51.57	13.586%	$58.5763	$58.58	$58.60	$58.60
7 purchase totals =	$605.57		$658.9442	$658.95	$658.90	$659.00