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	$47.92	13.778%	$54.5224	$54.52	$54.50	$54.50
Purchase #2	$87.57	6.492%	$93.255	$93.26	$93.25	$93.30
Purchase #3	$88.46	13.488%	$100.3915	$100.39	$100.40	$100.40
Purchase #4	$7.64	9.232%	$8.3453	$8.35	$8.35	$8.30
Purchase #5	$88.55	3.285%	$91.4589	$91.46	$91.45	$91.50
Purchase #6	$89.87	4.468%	$93.8854	$93.89	$93.90	$93.90
Purchase #7	$83.32	6.641%	$88.8533	$88.85	$88.85	$88.90
7 purchase totals =	$493.33		$530.7118	$530.72	$530.70	$530.80