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	$113.38	6.469%	$120.7146	$120.71	$120.70	$120.70
Purchase #2	$91.68	9.492%	$100.3823	$100.38	$100.40	$100.40
Purchase #3	$40.42	12.481%	$45.4648	$45.46	$45.45	$45.50
Purchase #4	$40.59	12.628%	$45.7157	$45.72	$45.70	$45.70
Purchase #5	$11.52	12.115%	$12.9156	$12.92	$12.90	$12.90
Purchase #6	$243.69	12.301%	$273.6663	$273.67	$273.65	$273.70
Purchase #7	$120.73	7.310%	$129.5554	$129.56	$129.55	$129.60
7 purchase totals =	$662.01		$728.4147	$728.42	$728.35	$728.50