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	$102.39	7.310%	$109.8747	$109.87	$109.85	$109.90
Purchase #2	$90.66	12.180%	$101.7024	$101.70	$101.70	$101.70
Purchase #3	$79.77	13.482%	$90.5246	$90.52	$90.50	$90.50
Purchase #4	$8.68	8.591%	$9.4257	$9.43	$9.45	$9.40
Purchase #5	$23.59	7.417%	$25.3397	$25.34	$25.35	$25.30
Purchase #6	$128.97	10.362%	$142.3339	$142.33	$142.35	$142.30
Purchase #7	$123.29	6.289%	$131.0437	$131.04	$131.05	$131.00
7 purchase totals =	$557.35		$610.2447	$610.23	$610.25	$610.10