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	$170.64	3.424%	$176.4827	$176.48	$176.50	$176.50
Purchase #2	$200.30	12.430%	$225.1973	$225.20	$225.20	$225.20
Purchase #3	$46.64	4.449%	$48.715	$48.72	$48.70	$48.70
Purchase #4	$190.72	4.512%	$199.3253	$199.33	$199.35	$199.30
Purchase #5	$53.92	3.601%	$55.8617	$55.86	$55.85	$55.90
Purchase #6	$10.37	6.397%	$11.0334	$11.03	$11.05	$11.00
Purchase #7	$80.27	12.502%	$90.3054	$90.31	$90.30	$90.30
7 purchase totals =	$752.86		$806.9208	$806.93	$806.95	$806.90