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	$33.84	13.334%	$38.3522	$38.35	$38.35	$38.40
Purchase #2	$153.74	12.503%	$172.9621	$172.96	$172.95	$173.00
Purchase #3	$39.43	7.629%	$42.4381	$42.44	$42.45	$42.40
Purchase #4	$208.43	6.281%	$221.5215	$221.52	$221.50	$221.50
Purchase #5	$74.59	3.707%	$77.3551	$77.36	$77.35	$77.40
Purchase #6	$67.63	6.160%	$71.796	$71.80	$71.80	$71.80
Purchase #7	$175.40	4.809%	$183.835	$183.84	$183.85	$183.80
7 purchase totals =	$753.06		$808.2600	$808.27	$808.25	$808.30