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	$192.44	9.288%	$210.3138	$210.31	$210.30	$210.30
Purchase #2	$131.36	3.178%	$135.5346	$135.53	$135.55	$135.50
Purchase #3	$136.49	6.153%	$144.8882	$144.89	$144.90	$144.90
Purchase #4	$36.81	6.321%	$39.1368	$39.14	$39.15	$39.10
Purchase #5	$233.42	12.626%	$262.8916	$262.89	$262.90	$262.90
Purchase #6	$115.41	10.549%	$127.5846	$127.58	$127.60	$127.60
Purchase #7	$74.39	12.361%	$83.5853	$83.59	$83.60	$83.60
7 purchase totals =	$920.32		$1,003.9349	$1,003.93	$1,004.00	$1,003.90