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	$172.97	7.669%	$186.2351	$186.24	$186.25	$186.20
Purchase #2	$90.70	9.479%	$99.2975	$99.30	$99.30	$99.30
Purchase #3	$89.73	11.714%	$100.241	$100.24	$100.25	$100.20
Purchase #4	$136.42	3.473%	$141.1579	$141.16	$141.15	$141.20
Purchase #5	$124.70	13.398%	$141.4073	$141.41	$141.40	$141.40
Purchase #6	$111.76	7.317%	$119.9375	$119.94	$119.95	$119.90
Purchase #7	$52.54	11.675%	$58.674	$58.67	$58.65	$58.70
7 purchase totals =	$778.82		$846.9503	$846.96	$846.95	$846.90