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	$100.33	4.493%	$104.8378	$104.84	$104.85	$104.80
Purchase #2	$239.72	11.635%	$267.6114	$267.61	$267.60	$267.60
Purchase #3	$18.92	6.749%	$20.1969	$20.20	$20.20	$20.20
Purchase #4	$55.41	11.649%	$61.8647	$61.86	$61.85	$61.90
Purchase #5	$6.49	11.380%	$7.2286	$7.23	$7.25	$7.20
Purchase #6	$53.37	13.327%	$60.4826	$60.48	$60.50	$60.50
Purchase #7	$246.41	11.816%	$275.5258	$275.53	$275.55	$275.50
7 purchase totals =	$720.65		$797.7478	$797.75	$797.80	$797.70