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	$37.52	6.639%	$40.011	$40.01	$40.00	$40.00
Purchase #2	$40.69	4.579%	$42.5532	$42.55	$42.55	$42.60
Purchase #3	$119.39	7.584%	$128.4445	$128.44	$128.45	$128.40
Purchase #4	$180.71	12.637%	$203.5463	$203.55	$203.55	$203.50
Purchase #5	$37.70	12.240%	$42.3145	$42.31	$42.30	$42.30
Purchase #6	$90.99	11.842%	$101.765	$101.77	$101.75	$101.80
Purchase #7	$105.60	4.650%	$110.5104	$110.51	$110.50	$110.50
7 purchase totals =	$612.60		$669.1449	$669.14	$669.10	$669.10