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	$55.85	3.642%	$57.8841	$57.88	$57.90	$57.90
Purchase #2	$80.69	10.825%	$89.4247	$89.42	$89.40	$89.40
Purchase #3	$125.73	3.176%	$129.7232	$129.72	$129.70	$129.70
Purchase #4	$181.34	5.578%	$191.4551	$191.46	$191.45	$191.50
Purchase #5	$148.78	8.413%	$161.2969	$161.30	$161.30	$161.30
Purchase #6	$142.84	10.406%	$157.7039	$157.70	$157.70	$157.70
Purchase #7	$233.93	10.643%	$258.8272	$258.83	$258.85	$258.80
7 purchase totals =	$969.16		$1,046.3151	$1,046.31	$1,046.30	$1,046.30