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	$193.37	7.838%	$208.5263	$208.53	$208.55	$208.50
Purchase #2	$144.68	10.814%	$160.3257	$160.33	$160.35	$160.30
Purchase #3	$111.81	7.604%	$120.312	$120.31	$120.30	$120.30
Purchase #4	$19.73	7.811%	$21.2711	$21.27	$21.25	$21.30
Purchase #5	$27.26	10.183%	$30.0359	$30.04	$30.05	$30.00
Purchase #6	$106.91	4.672%	$111.9048	$111.90	$111.90	$111.90
Purchase #7	$157.74	7.700%	$169.886	$169.89	$169.90	$169.90
7 purchase totals =	$761.50		$822.2618	$822.27	$822.30	$822.20