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	$146.88	3.837%	$152.5158	$152.52	$152.50	$152.50
Purchase #2	$216.30	9.245%	$236.2969	$236.30	$236.30	$236.30
Purchase #3	$127.76	11.755%	$142.7782	$142.78	$142.80	$142.80
Purchase #4	$201.43	13.683%	$228.9917	$228.99	$229.00	$229.00
Purchase #5	$246.43	11.778%	$275.4545	$275.45	$275.45	$275.50
Purchase #6	$197.61	13.285%	$223.8625	$223.86	$223.85	$223.90
Purchase #7	$135.35	3.777%	$140.4622	$140.46	$140.45	$140.50
7 purchase totals =	$1,271.76		$1,400.3618	$1,400.36	$1,400.35	$1,400.50