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	$60.34	6.534%	$64.2826	$64.28	$64.30	$64.30
Purchase #2	$241.85	3.720%	$250.8468	$250.85	$250.85	$250.80
Purchase #3	$185.66	7.126%	$198.8901	$198.89	$198.90	$198.90
Purchase #4	$175.71	3.279%	$181.4715	$181.47	$181.45	$181.50
Purchase #5	$25.60	8.261%	$27.7148	$27.71	$27.70	$27.70
Purchase #6	$99.40	7.739%	$107.0926	$107.09	$107.10	$107.10
Purchase #7	$212.56	4.871%	$222.9138	$222.91	$222.90	$222.90
7 purchase totals =	$1,001.12		$1,053.2122	$1,053.20	$1,053.20	$1,053.20