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	$57.77	11.295%	$64.2951	$64.30	$64.30	$64.30
Purchase #2	$115.89	12.540%	$130.4226	$130.42	$130.40	$130.40
Purchase #3	$140.63	4.779%	$147.3507	$147.35	$147.35	$147.40
Purchase #4	$120.98	8.547%	$131.3202	$131.32	$131.30	$131.30
Purchase #5	$120.45	6.547%	$128.3359	$128.34	$128.35	$128.30
Purchase #6	$102.34	9.113%	$111.6662	$111.67	$111.65	$111.70
Purchase #7	$180.81	3.690%	$187.4819	$187.48	$187.50	$187.50
7 purchase totals =	$838.87		$900.8726	$900.88	$900.85	$900.90