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	$139.31	12.294%	$156.4368	$156.44	$156.45	$156.40
Purchase #2	$111.34	12.384%	$125.1283	$125.13	$125.15	$125.10
Purchase #3	$6.66	11.394%	$7.4188	$7.42	$7.40	$7.40
Purchase #4	$187.90	3.864%	$195.1605	$195.16	$195.15	$195.20
Purchase #5	$178.78	7.124%	$191.5163	$191.52	$191.50	$191.50
Purchase #6	$143.94	6.525%	$153.3321	$153.33	$153.35	$153.30
Purchase #7	$162.86	7.470%	$175.0256	$175.03	$175.05	$175.00
7 purchase totals =	$930.79		$1,004.0184	$1,004.03	$1,004.05	$1,003.90