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	$39.66	7.430%	$42.6067	$42.61	$42.60	$42.60
Purchase #2	$53.36	11.514%	$59.5039	$59.50	$59.50	$59.50
Purchase #3	$74.55	12.173%	$83.625	$83.63	$83.65	$83.60
Purchase #4	$222.46	10.330%	$245.4401	$245.44	$245.45	$245.40
Purchase #5	$74.49	11.745%	$83.2389	$83.24	$83.25	$83.20
Purchase #6	$198.87	5.422%	$209.6527	$209.65	$209.65	$209.70
Purchase #7	$129.91	12.770%	$146.4995	$146.50	$146.50	$146.50
7 purchase totals =	$793.30		$870.5668	$870.57	$870.60	$870.50