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	$241.27	12.442%	$271.2888	$271.29	$271.30	$271.30
Purchase #2	$82.96	8.263%	$89.815	$89.82	$89.80	$89.80
Purchase #3	$95.94	11.222%	$106.7064	$106.71	$106.70	$106.70
Purchase #4	$171.62	6.502%	$182.7787	$182.78	$182.80	$182.80
Purchase #5	$109.68	4.380%	$114.484	$114.48	$114.50	$114.50
Purchase #6	$130.25	5.481%	$137.389	$137.39	$137.40	$137.40
Purchase #7	$17.66	9.607%	$19.3566	$19.36	$19.35	$19.40
7 purchase totals =	$849.38		$921.8185	$921.83	$921.85	$921.90