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	$189.55	7.174%	$203.1483	$203.15	$203.15	$203.10
Purchase #2	$214.56	10.288%	$236.6339	$236.63	$236.65	$236.60
Purchase #3	$219.34	11.308%	$244.143	$244.14	$244.15	$244.10
Purchase #4	$82.61	7.263%	$88.61	$88.61	$88.60	$88.60
Purchase #5	$83.33	6.593%	$88.8239	$88.82	$88.80	$88.80
Purchase #6	$176.72	13.507%	$200.5896	$200.59	$200.60	$200.60
Purchase #7	$33.40	13.111%	$37.7791	$37.78	$37.80	$37.80
7 purchase totals =	$999.51		$1,099.7278	$1,099.72	$1,099.75	$1,099.60