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	$57.40	5.103%	$60.3291	$60.33	$60.35	$60.30
Purchase #2	$115.56	4.492%	$120.751	$120.75	$120.75	$120.80
Purchase #3	$66.44	9.292%	$72.6136	$72.61	$72.60	$72.60
Purchase #4	$85.51	11.770%	$95.5745	$95.57	$95.55	$95.60
Purchase #5	$20.64	7.786%	$22.247	$22.25	$22.25	$22.20
Purchase #6	$182.56	8.652%	$198.3551	$198.36	$198.35	$198.40
Purchase #7	$37.72	12.692%	$42.5074	$42.51	$42.50	$42.50
7 purchase totals =	$565.83		$612.3777	$612.38	$612.35	$612.40