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	$80.36	13.426%	$91.1491	$91.15	$91.15	$91.10
Purchase #2	$46.85	4.755%	$49.0777	$49.08	$49.10	$49.10
Purchase #3	$243.62	12.191%	$273.3197	$273.32	$273.30	$273.30
Purchase #4	$63.82	11.445%	$71.1242	$71.12	$71.10	$71.10
Purchase #5	$161.74	6.223%	$171.8051	$171.81	$171.80	$171.80
Purchase #6	$151.73	9.741%	$166.51	$166.51	$166.50	$166.50
Purchase #7	$144.77	13.295%	$164.0172	$164.02	$164.00	$164.00
7 purchase totals =	$892.89		$987.0030	$987.01	$986.95	$986.90