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	$155.62	10.361%	$171.7438	$171.74	$171.75	$171.70
Purchase #2	$58.80	9.261%	$64.2455	$64.25	$64.25	$64.20
Purchase #3	$40.86	4.392%	$42.6546	$42.65	$42.65	$42.70
Purchase #4	$192.58	3.359%	$199.0488	$199.05	$199.05	$199.00
Purchase #5	$99.98	11.846%	$111.8236	$111.82	$111.80	$111.80
Purchase #6	$55.98	8.661%	$60.8284	$60.83	$60.85	$60.80
Purchase #7	$175.77	7.809%	$189.4959	$189.50	$189.50	$189.50
7 purchase totals =	$779.59		$839.8406	$839.84	$839.85	$839.70