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	$145.61	5.258%	$153.2662	$153.27	$153.25	$153.30
Purchase #2	$156.97	4.428%	$163.9206	$163.92	$163.90	$163.90
Purchase #3	$11.71	10.228%	$12.9077	$12.91	$12.90	$12.90
Purchase #4	$97.91	11.350%	$109.0228	$109.02	$109.00	$109.00
Purchase #5	$72.69	7.140%	$77.8801	$77.88	$77.90	$77.90
Purchase #6	$150.25	12.382%	$168.854	$168.85	$168.85	$168.90
Purchase #7	$94.34	13.301%	$106.8882	$106.89	$106.90	$106.90
7 purchase totals =	$729.48		$792.7396	$792.74	$792.70	$792.80