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	$104.43	3.151%	$107.7206	$107.72	$107.70	$107.70
Purchase #2	$91.78	7.546%	$98.7057	$98.71	$98.70	$98.70
Purchase #3	$92.64	7.194%	$99.3045	$99.30	$99.30	$99.30
Purchase #4	$35.65	12.753%	$40.1964	$40.20	$40.20	$40.20
Purchase #5	$216.79	10.203%	$238.9091	$238.91	$238.90	$238.90
Purchase #6	$95.96	9.238%	$104.8248	$104.82	$104.80	$104.80
Purchase #7	$197.50	6.716%	$210.7641	$210.76	$210.75	$210.80
7 purchase totals =	$834.75		$900.4252	$900.42	$900.35	$900.40