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	$64.87	10.470%	$71.6619	$71.66	$71.65	$71.70
Purchase #2	$135.73	11.183%	$150.9087	$150.91	$150.90	$150.90
Purchase #3	$79.85	7.362%	$85.7286	$85.73	$85.75	$85.70
Purchase #4	$132.91	13.661%	$151.0668	$151.07	$151.05	$151.10
Purchase #5	$6.85	10.204%	$7.549	$7.55	$7.55	$7.50
Purchase #6	$64.87	9.454%	$71.0028	$71.00	$71.00	$71.00
Purchase #7	$40.76	3.538%	$42.2021	$42.20	$42.20	$42.20
7 purchase totals =	$525.84		$580.1199	$580.12	$580.10	$580.10