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	$149.84	10.140%	$165.0338	$165.03	$165.05	$165.00
Purchase #2	$35.44	7.778%	$38.1965	$38.20	$38.20	$38.20
Purchase #3	$128.63	10.803%	$142.5259	$142.53	$142.55	$142.50
Purchase #4	$236.71	4.735%	$247.9182	$247.92	$247.90	$247.90
Purchase #5	$231.92	9.507%	$253.9686	$253.97	$253.95	$254.00
Purchase #6	$78.50	5.352%	$82.7013	$82.70	$82.70	$82.70
Purchase #7	$49.30	3.208%	$50.8815	$50.88	$50.90	$50.90
7 purchase totals =	$910.34		$981.2258	$981.23	$981.25	$981.20