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	$234.28	7.121%	$250.9631	$250.96	$250.95	$251.00
Purchase #2	$51.79	4.822%	$54.2873	$54.29	$54.30	$54.30
Purchase #3	$250.89	13.294%	$284.2433	$284.24	$284.25	$284.20
Purchase #4	$172.72	5.380%	$182.0123	$182.01	$182.00	$182.00
Purchase #5	$59.58	3.533%	$61.685	$61.69	$61.70	$61.70
Purchase #6	$199.88	12.242%	$224.3493	$224.35	$224.35	$224.30
Purchase #7	$90.78	10.467%	$100.2819	$100.28	$100.30	$100.30
7 purchase totals =	$1,059.92		$1,157.8222	$1,157.82	$1,157.85	$1,157.80