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	$82.92	7.577%	$89.2028	$89.20	$89.20	$89.20
Purchase #2	$16.70	8.151%	$18.0612	$18.06	$18.05	$18.10
Purchase #3	$78.33	6.480%	$83.4058	$83.41	$83.40	$83.40
Purchase #4	$229.47	6.108%	$243.486	$243.49	$243.50	$243.50
Purchase #5	$247.94	7.269%	$265.9628	$265.96	$265.95	$266.00
Purchase #6	$194.54	8.337%	$210.7588	$210.76	$210.75	$210.80
Purchase #7	$223.89	9.257%	$244.6155	$244.62	$244.60	$244.60
7 purchase totals =	$1,073.79		$1,155.4929	$1,155.50	$1,155.45	$1,155.60