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	$87.48	13.578%	$99.358	$99.36	$99.35	$99.40
Purchase #2	$202.41	11.393%	$225.4706	$225.47	$225.45	$225.50
Purchase #3	$99.58	10.323%	$109.8596	$109.86	$109.85	$109.90
Purchase #4	$77.47	8.121%	$83.7613	$83.76	$83.75	$83.80
Purchase #5	$64.51	3.336%	$66.6621	$66.66	$66.65	$66.70
Purchase #6	$228.30	5.742%	$241.409	$241.41	$241.40	$241.40
Purchase #7	$83.53	9.471%	$91.4411	$91.44	$91.45	$91.40
7 purchase totals =	$843.28		$917.9617	$917.96	$917.90	$918.10