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	$211.79	3.656%	$219.533	$219.53	$219.55	$219.50
Purchase #2	$55.89	7.614%	$60.1455	$60.15	$60.15	$60.10
Purchase #3	$52.83	7.848%	$56.9761	$56.98	$57.00	$57.00
Purchase #4	$40.47	9.741%	$44.4122	$44.41	$44.40	$44.40
Purchase #5	$66.72	10.217%	$73.5368	$73.54	$73.55	$73.50
Purchase #6	$42.98	5.441%	$45.3185	$45.32	$45.30	$45.30
Purchase #7	$39.37	5.227%	$41.4279	$41.43	$41.45	$41.40
7 purchase totals =	$510.05		$541.3500	$541.36	$541.40	$541.20