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	$39.29	3.828%	$40.794	$40.79	$40.80	$40.80
Purchase #2	$173.45	3.533%	$179.578	$179.58	$179.60	$179.60
Purchase #3	$94.86	5.141%	$99.7368	$99.74	$99.75	$99.70
Purchase #4	$134.48	7.572%	$144.6628	$144.66	$144.65	$144.70
Purchase #5	$225.36	12.686%	$253.9492	$253.95	$253.95	$253.90
Purchase #6	$213.55	12.705%	$240.6815	$240.68	$240.70	$240.70
Purchase #7	$233.52	7.110%	$250.1233	$250.12	$250.10	$250.10
7 purchase totals =	$1,114.51		$1,209.5256	$1,209.52	$1,209.55	$1,209.50