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	$35.72	4.394%	$37.2895	$37.29	$37.30	$37.30
Purchase #2	$128.87	5.828%	$136.3805	$136.38	$136.40	$136.40
Purchase #3	$29.69	8.704%	$32.2742	$32.27	$32.25	$32.30
Purchase #4	$114.61	4.107%	$119.317	$119.32	$119.30	$119.30
Purchase #5	$221.44	13.111%	$250.473	$250.47	$250.45	$250.50
Purchase #6	$96.94	3.834%	$100.6567	$100.66	$100.65	$100.70
Purchase #7	$171.86	11.211%	$191.1272	$191.13	$191.15	$191.10
7 purchase totals =	$799.13		$867.5181	$867.52	$867.50	$867.60