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	$29.53	3.234%	$30.485	$30.49	$30.50	$30.50
Purchase #2	$191.53	9.585%	$209.8882	$209.89	$209.90	$209.90
Purchase #3	$199.30	8.752%	$216.7427	$216.74	$216.75	$216.70
Purchase #4	$237.38	10.642%	$262.642	$262.64	$262.65	$262.60
Purchase #5	$213.29	4.849%	$223.6324	$223.63	$223.65	$223.60
Purchase #6	$241.89	5.791%	$255.8978	$255.90	$255.90	$255.90
Purchase #7	$214.80	8.816%	$233.7368	$233.74	$233.75	$233.70
7 purchase totals =	$1,327.72		$1,433.0249	$1,433.03	$1,433.10	$1,432.90