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	$236.36	12.443%	$265.7703	$265.77	$265.75	$265.80
Purchase #2	$112.40	13.689%	$127.7864	$127.79	$127.80	$127.80
Purchase #3	$104.48	9.511%	$114.4171	$114.42	$114.40	$114.40
Purchase #4	$231.39	6.676%	$246.8376	$246.84	$246.85	$246.80
Purchase #5	$60.74	6.801%	$64.8709	$64.87	$64.85	$64.90
Purchase #6	$244.64	3.818%	$253.9804	$253.98	$254.00	$254.00
Purchase #7	$59.28	11.126%	$65.8755	$65.88	$65.90	$65.90
7 purchase totals =	$1,049.29		$1,139.5382	$1,139.55	$1,139.55	$1,139.60