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	$91.96	7.681%	$99.0234	$99.02	$99.00	$99.00
Purchase #2	$44.73	13.598%	$50.8124	$50.81	$50.80	$50.80
Purchase #3	$91.94	13.311%	$104.1781	$104.18	$104.20	$104.20
Purchase #4	$19.42	4.167%	$20.2292	$20.23	$20.25	$20.20
Purchase #5	$85.82	11.405%	$95.6078	$95.61	$95.60	$95.60
Purchase #6	$136.92	7.366%	$147.0055	$147.01	$147.00	$147.00
Purchase #7	$49.72	8.366%	$53.8796	$53.88	$53.90	$53.90
7 purchase totals =	$520.51		$570.7360	$570.74	$570.75	$570.70