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	$78.70	13.331%	$89.1915	$89.19	$89.20	$89.20
Purchase #2	$20.58	8.782%	$22.3873	$22.39	$22.40	$22.40
Purchase #3	$94.63	12.712%	$106.6594	$106.66	$106.65	$106.70
Purchase #4	$247.43	6.219%	$262.8177	$262.82	$262.80	$262.80
Purchase #5	$20.25	3.221%	$20.9023	$20.90	$20.90	$20.90
Purchase #6	$245.26	4.118%	$255.3598	$255.36	$255.35	$255.40
Purchase #7	$61.83	6.507%	$65.8533	$65.85	$65.85	$65.90
7 purchase totals =	$768.68		$823.1713	$823.17	$823.15	$823.30