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	$172.76	4.205%	$180.0246	$180.02	$180.00	$180.00
Purchase #2	$37.75	12.394%	$42.4287	$42.43	$42.45	$42.40
Purchase #3	$241.48	13.537%	$274.1691	$274.17	$274.15	$274.20
Purchase #4	$188.84	10.403%	$208.485	$208.49	$208.50	$208.50
Purchase #5	$247.53	10.547%	$273.637	$273.64	$273.65	$273.60
Purchase #6	$75.79	12.487%	$85.2539	$85.25	$85.25	$85.30
Purchase #7	$39.40	7.344%	$42.2935	$42.29	$42.30	$42.30
7 purchase totals =	$1,003.55		$1,106.2918	$1,106.29	$1,106.30	$1,106.30