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	$12.56	4.663%	$13.1457	$13.15	$13.15	$13.10
Purchase #2	$124.96	13.587%	$141.9383	$141.94	$141.95	$141.90
Purchase #3	$36.87	6.118%	$39.1257	$39.13	$39.15	$39.10
Purchase #4	$88.70	4.145%	$92.3766	$92.38	$92.40	$92.40
Purchase #5	$162.45	12.581%	$182.8878	$182.89	$182.90	$182.90
Purchase #6	$59.44	3.618%	$61.5905	$61.59	$61.60	$61.60
Purchase #7	$8.85	11.313%	$9.8512	$9.85	$9.85	$9.90
7 purchase totals =	$493.83		$540.9158	$540.93	$541.00	$540.90