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	$171.87	11.756%	$192.075	$192.08	$192.10	$192.10
Purchase #2	$131.76	8.567%	$143.0479	$143.05	$143.05	$143.00
Purchase #3	$118.57	4.615%	$124.042	$124.04	$124.05	$124.00
Purchase #4	$154.85	6.480%	$164.8843	$164.88	$164.90	$164.90
Purchase #5	$159.74	7.322%	$171.4362	$171.44	$171.45	$171.40
Purchase #6	$33.57	10.564%	$37.1163	$37.12	$37.10	$37.10
Purchase #7	$36.94	9.693%	$40.5206	$40.52	$40.50	$40.50
7 purchase totals =	$807.30		$873.1223	$873.13	$873.15	$873.00