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	$30.27	6.427%	$32.2155	$32.22	$32.20	$32.20
Purchase #2	$40.29	4.578%	$42.1345	$42.13	$42.15	$42.10
Purchase #3	$137.57	3.706%	$142.6683	$142.67	$142.65	$142.70
Purchase #4	$106.46	6.567%	$113.4512	$113.45	$113.45	$113.50
Purchase #5	$73.91	9.862%	$81.199	$81.20	$81.20	$81.20
Purchase #6	$35.28	12.241%	$39.5986	$39.60	$39.60	$39.60
Purchase #7	$130.91	9.655%	$143.5494	$143.55	$143.55	$143.50
7 purchase totals =	$554.69		$594.8165	$594.82	$594.80	$594.80