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	$35.92	6.579%	$38.2832	$38.28	$38.30	$38.30
Purchase #2	$229.81	3.132%	$237.0076	$237.01	$237.00	$237.00
Purchase #3	$73.42	12.162%	$82.3493	$82.35	$82.35	$82.30
Purchase #4	$99.53	4.814%	$104.3214	$104.32	$104.30	$104.30
Purchase #5	$203.28	9.632%	$222.8599	$222.86	$222.85	$222.90
Purchase #6	$168.61	13.550%	$191.4567	$191.46	$191.45	$191.50
Purchase #7	$231.63	4.765%	$242.6672	$242.67	$242.65	$242.70
7 purchase totals =	$1,042.20		$1,118.9453	$1,118.95	$1,118.90	$1,119.00