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	$107.41	4.644%	$112.3981	$112.40	$112.40	$112.40
Purchase #2	$109.32	6.501%	$116.4269	$116.43	$116.45	$116.40
Purchase #3	$218.91	11.232%	$243.498	$243.50	$243.50	$243.50
Purchase #4	$172.28	5.682%	$182.0689	$182.07	$182.05	$182.10
Purchase #5	$227.90	8.713%	$247.7569	$247.76	$247.75	$247.80
Purchase #6	$185.32	5.851%	$196.1631	$196.16	$196.15	$196.20
Purchase #7	$128.34	12.355%	$144.1964	$144.20	$144.20	$144.20
7 purchase totals =	$1,149.48		$1,242.5083	$1,242.52	$1,242.50	$1,242.60