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	$98.30	8.652%	$106.8049	$106.80	$106.80	$106.80
Purchase #2	$6.30	11.691%	$7.0365	$7.04	$7.05	$7.00
Purchase #3	$237.30	9.789%	$260.5293	$260.53	$260.55	$260.50
Purchase #4	$127.76	7.822%	$137.7534	$137.75	$137.75	$137.80
Purchase #5	$247.72	7.740%	$266.8935	$266.89	$266.90	$266.90
Purchase #6	$92.59	3.589%	$95.9131	$95.91	$95.90	$95.90
Purchase #7	$199.51	3.711%	$206.9138	$206.91	$206.90	$206.90
7 purchase totals =	$1,009.48		$1,081.8445	$1,081.83	$1,081.85	$1,081.80