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	$40.75	11.659%	$45.501	$45.50	$45.50	$45.50
Purchase #2	$221.72	12.761%	$250.0137	$250.01	$250.00	$250.00
Purchase #3	$66.64	3.709%	$69.1117	$69.11	$69.10	$69.10
Purchase #4	$46.96	7.161%	$50.3228	$50.32	$50.30	$50.30
Purchase #5	$150.73	5.355%	$158.8016	$158.80	$158.80	$158.80
Purchase #6	$100.55	9.507%	$110.1093	$110.11	$110.10	$110.10
Purchase #7	$72.39	6.107%	$76.8109	$76.81	$76.80	$76.80
7 purchase totals =	$699.74		$760.6710	$760.66	$760.60	$760.60