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	$18.42	11.775%	$20.589	$20.59	$20.60	$20.60
Purchase #2	$206.87	8.211%	$223.8561	$223.86	$223.85	$223.90
Purchase #3	$22.52	12.700%	$25.38	$25.38	$25.40	$25.40
Purchase #4	$80.50	11.633%	$89.8646	$89.86	$89.85	$89.90
Purchase #5	$169.69	13.623%	$192.8069	$192.81	$192.80	$192.80
Purchase #6	$42.51	6.612%	$45.3208	$45.32	$45.30	$45.30
Purchase #7	$186.38	4.774%	$195.2778	$195.28	$195.30	$195.30
7 purchase totals =	$726.89		$793.0952	$793.10	$793.10	$793.20