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	$19.60	5.842%	$20.745	$20.75	$20.75	$20.70
Purchase #2	$180.55	4.345%	$188.3949	$188.39	$188.40	$188.40
Purchase #3	$232.43	7.761%	$250.4689	$250.47	$250.45	$250.50
Purchase #4	$37.73	9.616%	$41.3581	$41.36	$41.35	$41.40
Purchase #5	$204.43	8.827%	$222.475	$222.48	$222.50	$222.50
Purchase #6	$143.78	8.669%	$156.2443	$156.24	$156.25	$156.20
Purchase #7	$247.34	12.132%	$277.3473	$277.35	$277.35	$277.30
7 purchase totals =	$1,065.86		$1,157.0335	$1,157.04	$1,157.05	$1,157.00