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	$64.58	11.742%	$72.163	$72.16	$72.15	$72.20
Purchase #2	$165.61	12.858%	$186.9041	$186.90	$186.90	$186.90
Purchase #3	$168.53	7.853%	$181.7647	$181.76	$181.75	$181.80
Purchase #4	$135.52	8.280%	$146.7411	$146.74	$146.75	$146.70
Purchase #5	$247.79	10.639%	$274.1524	$274.15	$274.15	$274.20
Purchase #6	$138.85	9.693%	$152.3087	$152.31	$152.30	$152.30
Purchase #7	$236.96	12.564%	$266.7317	$266.73	$266.75	$266.70
7 purchase totals =	$1,157.84		$1,280.7657	$1,280.75	$1,280.75	$1,280.80