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	$28.49	10.214%	$31.4	$31.40	$31.40	$31.40
Purchase #2	$149.78	9.707%	$164.3191	$164.32	$164.30	$164.30
Purchase #3	$183.58	6.847%	$196.1497	$196.15	$196.15	$196.10
Purchase #4	$158.42	7.778%	$170.7419	$170.74	$170.75	$170.70
Purchase #5	$51.94	7.274%	$55.7181	$55.72	$55.70	$55.70
Purchase #6	$137.28	10.800%	$152.1062	$152.11	$152.10	$152.10
Purchase #7	$171.36	5.174%	$180.2262	$180.23	$180.25	$180.20
7 purchase totals =	$880.85		$950.6612	$950.67	$950.65	$950.50