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	$73.33	13.497%	$83.2274	$83.23	$83.25	$83.20
Purchase #2	$250.53	13.656%	$284.7424	$284.74	$284.75	$284.70
Purchase #3	$176.51	10.705%	$195.4054	$195.41	$195.40	$195.40
Purchase #4	$78.48	4.833%	$82.2729	$82.27	$82.25	$82.30
Purchase #5	$98.64	12.661%	$111.1288	$111.13	$111.15	$111.10
Purchase #6	$102.69	10.844%	$113.8257	$113.83	$113.85	$113.80
Purchase #7	$129.77	8.652%	$140.9977	$141.00	$141.00	$141.00
7 purchase totals =	$909.95		$1,011.6003	$1,011.61	$1,011.65	$1,011.50