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	$44.92	9.849%	$49.3442	$49.34	$49.35	$49.30
Purchase #2	$161.85	12.378%	$181.8838	$181.88	$181.90	$181.90
Purchase #3	$28.33	11.653%	$31.6313	$31.63	$31.65	$31.60
Purchase #4	$209.59	6.166%	$222.5133	$222.51	$222.50	$222.50
Purchase #5	$222.34	12.647%	$250.4593	$250.46	$250.45	$250.50
Purchase #6	$67.30	13.259%	$76.2233	$76.22	$76.20	$76.20
Purchase #7	$58.67	3.364%	$60.6437	$60.64	$60.65	$60.60
7 purchase totals =	$793.00		$872.6989	$872.68	$872.70	$872.60