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	$170.50	12.245%	$191.3777	$191.38	$191.40	$191.40
Purchase #2	$128.69	13.400%	$145.9345	$145.93	$145.95	$145.90
Purchase #3	$187.89	3.768%	$194.9697	$194.97	$194.95	$195.00
Purchase #4	$96.48	9.276%	$105.4295	$105.43	$105.45	$105.40
Purchase #5	$98.46	4.449%	$102.8405	$102.84	$102.85	$102.80
Purchase #6	$182.50	9.700%	$200.2025	$200.20	$200.20	$200.20
Purchase #7	$138.68	5.152%	$145.8248	$145.82	$145.80	$145.80
7 purchase totals =	$1,003.20		$1,086.5792	$1,086.57	$1,086.60	$1,086.50