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	$100.73	8.559%	$109.3515	$109.35	$109.35	$109.40
Purchase #2	$69.40	6.722%	$74.0651	$74.07	$74.05	$74.10
Purchase #3	$114.34	9.859%	$125.6128	$125.61	$125.60	$125.60
Purchase #4	$80.47	11.297%	$89.5607	$89.56	$89.55	$89.60
Purchase #5	$171.37	8.252%	$185.5115	$185.51	$185.50	$185.50
Purchase #6	$142.44	5.554%	$150.3511	$150.35	$150.35	$150.40
Purchase #7	$137.45	12.298%	$154.3536	$154.35	$154.35	$154.40
7 purchase totals =	$816.20		$888.8063	$888.80	$888.75	$889.00