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	$82.83	13.750%	$94.2191	$94.22	$94.20	$94.20
Purchase #2	$83.67	8.466%	$90.7535	$90.75	$90.75	$90.80
Purchase #3	$101.78	6.172%	$108.0619	$108.06	$108.05	$108.10
Purchase #4	$228.95	6.185%	$243.1106	$243.11	$243.10	$243.10
Purchase #5	$25.31	11.153%	$28.1328	$28.13	$28.15	$28.10
Purchase #6	$246.86	8.427%	$267.6629	$267.66	$267.65	$267.70
Purchase #7	$151.32	13.400%	$171.5969	$171.60	$171.60	$171.60
7 purchase totals =	$920.72		$1,003.5377	$1,003.53	$1,003.50	$1,003.60