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	$51.44	6.620%	$54.8453	$54.85	$54.85	$54.80
Purchase #2	$245.65	11.580%	$274.0963	$274.10	$274.10	$274.10
Purchase #3	$144.67	3.833%	$150.2152	$150.22	$150.20	$150.20
Purchase #4	$33.67	13.280%	$38.1414	$38.14	$38.15	$38.10
Purchase #5	$141.33	4.173%	$147.2277	$147.23	$147.25	$147.20
Purchase #6	$87.47	6.865%	$93.4748	$93.47	$93.45	$93.50
Purchase #7	$238.29	6.749%	$254.3722	$254.37	$254.35	$254.40
7 purchase totals =	$942.52		$1,012.3729	$1,012.38	$1,012.35	$1,012.30