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	$100.70	8.856%	$109.618	$109.62	$109.60	$109.60
Purchase #2	$172.46	12.686%	$194.3383	$194.34	$194.35	$194.30
Purchase #3	$118.98	7.541%	$127.9523	$127.95	$127.95	$128.00
Purchase #4	$213.54	8.126%	$230.8923	$230.89	$230.90	$230.90
Purchase #5	$52.54	10.532%	$58.0735	$58.07	$58.05	$58.10
Purchase #6	$147.48	12.277%	$165.5861	$165.59	$165.60	$165.60
Purchase #7	$199.60	3.631%	$206.8475	$206.85	$206.85	$206.80
7 purchase totals =	$1,005.30		$1,093.3080	$1,093.31	$1,093.30	$1,093.30