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	$188.57	12.580%	$212.2921	$212.29	$212.30	$212.30
Purchase #2	$172.50	7.527%	$185.4841	$185.48	$185.50	$185.50
Purchase #3	$125.42	10.154%	$138.1551	$138.16	$138.15	$138.20
Purchase #4	$77.37	10.371%	$85.394	$85.39	$85.40	$85.40
Purchase #5	$246.90	8.779%	$268.5754	$268.58	$268.60	$268.60
Purchase #6	$75.49	9.840%	$82.9182	$82.92	$82.90	$82.90
Purchase #7	$146.49	6.225%	$155.609	$155.61	$155.60	$155.60
7 purchase totals =	$1,032.74		$1,128.4279	$1,128.43	$1,128.45	$1,128.50