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	$130.41	8.275%	$141.2014	$141.20	$141.20	$141.20
Purchase #2	$33.54	4.393%	$35.0134	$35.01	$35.00	$35.00
Purchase #3	$83.92	7.499%	$90.2132	$90.21	$90.20	$90.20
Purchase #4	$209.42	13.681%	$238.0708	$238.07	$238.05	$238.10
Purchase #5	$92.51	13.395%	$104.9017	$104.90	$104.90	$104.90
Purchase #6	$131.41	6.820%	$140.3722	$140.37	$140.35	$140.40
Purchase #7	$212.73	6.478%	$226.5106	$226.51	$226.50	$226.50
7 purchase totals =	$893.94		$976.2833	$976.27	$976.20	$976.30