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	$74.75	4.422%	$78.0554	$78.06	$78.05	$78.10
Purchase #2	$97.82	8.400%	$106.0369	$106.04	$106.05	$106.00
Purchase #3	$57.38	4.336%	$59.868	$59.87	$59.85	$59.90
Purchase #4	$147.63	7.186%	$158.2387	$158.24	$158.25	$158.20
Purchase #5	$92.75	10.505%	$102.4934	$102.49	$102.50	$102.50
Purchase #6	$79.36	13.427%	$90.0157	$90.02	$90.00	$90.00
Purchase #7	$24.66	4.454%	$25.7584	$25.76	$25.75	$25.80
7 purchase totals =	$574.35		$620.4665	$620.48	$620.45	$620.50