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	$122.85	10.281%	$135.4802	$135.48	$135.50	$135.50
Purchase #2	$43.96	13.331%	$49.8203	$49.82	$49.80	$49.80
Purchase #3	$240.96	6.600%	$256.8634	$256.86	$256.85	$256.90
Purchase #4	$137.56	10.477%	$151.9722	$151.97	$151.95	$152.00
Purchase #5	$195.80	11.253%	$217.8334	$217.83	$217.85	$217.80
Purchase #6	$35.26	7.799%	$38.0099	$38.01	$38.00	$38.00
Purchase #7	$236.92	7.773%	$255.3358	$255.34	$255.35	$255.30
7 purchase totals =	$1,013.31		$1,105.3152	$1,105.31	$1,105.30	$1,105.30