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	$32.34	8.598%	$35.1206	$35.12	$35.10	$35.10
Purchase #2	$179.52	3.494%	$185.7924	$185.79	$185.80	$185.80
Purchase #3	$38.57	11.138%	$42.8659	$42.87	$42.85	$42.90
Purchase #4	$229.51	6.463%	$244.3432	$244.34	$244.35	$244.30
Purchase #5	$31.30	4.564%	$32.7285	$32.73	$32.75	$32.70
Purchase #6	$152.70	5.382%	$160.9183	$160.92	$160.90	$160.90
Purchase #7	$181.88	10.107%	$200.2626	$200.26	$200.25	$200.30
7 purchase totals =	$845.82		$902.0315	$902.03	$902.00	$902.00