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	$10.78	11.612%	$12.0318	$12.03	$12.05	$12.00
Purchase #2	$98.36	11.499%	$109.6704	$109.67	$109.65	$109.70
Purchase #3	$172.48	9.816%	$189.4106	$189.41	$189.40	$189.40
Purchase #4	$91.45	11.477%	$101.9457	$101.95	$101.95	$101.90
Purchase #5	$34.33	7.848%	$37.0242	$37.02	$37.00	$37.00
Purchase #6	$119.65	12.297%	$134.3634	$134.36	$134.35	$134.40
Purchase #7	$69.73	11.698%	$77.887	$77.89	$77.90	$77.90
7 purchase totals =	$596.78		$662.3331	$662.33	$662.30	$662.30