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	$139.82	12.815%	$157.7379	$157.74	$157.75	$157.70
Purchase #2	$168.29	12.242%	$188.8921	$188.89	$188.90	$188.90
Purchase #3	$54.61	9.739%	$59.9285	$59.93	$59.95	$59.90
Purchase #4	$209.85	8.382%	$227.4396	$227.44	$227.45	$227.40
Purchase #5	$179.66	11.703%	$200.6856	$200.69	$200.70	$200.70
Purchase #6	$83.26	9.400%	$91.0864	$91.09	$91.10	$91.10
Purchase #7	$46.69	8.746%	$50.7735	$50.77	$50.75	$50.80
7 purchase totals =	$882.18		$976.5436	$976.55	$976.60	$976.50