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	$188.28	5.852%	$199.2981	$199.30	$199.30	$199.30
Purchase #2	$156.56	9.466%	$171.38	$171.38	$171.40	$171.40
Purchase #3	$37.50	12.860%	$42.3225	$42.32	$42.30	$42.30
Purchase #4	$35.69	9.669%	$39.1409	$39.14	$39.15	$39.10
Purchase #5	$119.92	8.414%	$130.0101	$130.01	$130.00	$130.00
Purchase #6	$209.46	11.665%	$233.8935	$233.89	$233.90	$233.90
Purchase #7	$91.69	13.455%	$104.0269	$104.03	$104.05	$104.00
7 purchase totals =	$839.10		$920.0720	$920.07	$920.10	$920.00