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	$96.33	7.594%	$103.6453	$103.65	$103.65	$103.60
Purchase #2	$79.64	12.368%	$89.4899	$89.49	$89.50	$89.50
Purchase #3	$204.54	9.817%	$224.6197	$224.62	$224.60	$224.60
Purchase #4	$134.31	10.281%	$148.1184	$148.12	$148.10	$148.10
Purchase #5	$139.45	9.355%	$152.4955	$152.50	$152.50	$152.50
Purchase #6	$139.42	10.257%	$153.7203	$153.72	$153.70	$153.70
Purchase #7	$81.70	3.372%	$84.4549	$84.45	$84.45	$84.50
7 purchase totals =	$875.39		$956.5440	$956.55	$956.50	$956.50