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	$222.34	9.274%	$242.9598	$242.96	$242.95	$243.00
Purchase #2	$69.25	12.710%	$78.0517	$78.05	$78.05	$78.10
Purchase #3	$182.48	9.229%	$199.3211	$199.32	$199.30	$199.30
Purchase #4	$72.65	13.348%	$82.3473	$82.35	$82.35	$82.30
Purchase #5	$97.95	4.404%	$102.2637	$102.26	$102.25	$102.30
Purchase #6	$107.58	13.320%	$121.9097	$121.91	$121.90	$121.90
Purchase #7	$237.35	7.372%	$254.8474	$254.85	$254.85	$254.80
7 purchase totals =	$989.60		$1,081.7007	$1,081.70	$1,081.65	$1,081.70