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	$197.91	12.632%	$222.91	$222.91	$222.90	$222.90
Purchase #2	$195.70	13.735%	$222.5794	$222.58	$222.60	$222.60
Purchase #3	$25.77	9.654%	$28.2578	$28.26	$28.25	$28.30
Purchase #4	$29.67	8.470%	$32.183	$32.18	$32.20	$32.20
Purchase #5	$28.33	4.764%	$29.6796	$29.68	$29.70	$29.70
Purchase #6	$70.56	10.609%	$78.0457	$78.05	$78.05	$78.00
Purchase #7	$223.95	6.319%	$238.1014	$238.10	$238.10	$238.10
7 purchase totals =	$771.89		$851.7569	$851.76	$851.80	$851.80