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	$85.66	6.681%	$91.3829	$91.38	$91.40	$91.40
Purchase #2	$147.89	13.683%	$168.1258	$168.13	$168.15	$168.10
Purchase #3	$57.89	7.692%	$62.3429	$62.34	$62.35	$62.30
Purchase #4	$141.71	4.461%	$148.0317	$148.03	$148.05	$148.00
Purchase #5	$81.39	6.687%	$86.8325	$86.83	$86.85	$86.80
Purchase #6	$12.59	8.111%	$13.6112	$13.61	$13.60	$13.60
Purchase #7	$191.36	4.637%	$200.2334	$200.23	$200.25	$200.20
7 purchase totals =	$718.49		$770.5604	$770.55	$770.65	$770.40