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	$166.81	12.290%	$187.3109	$187.31	$187.30	$187.30
Purchase #2	$108.60	7.562%	$116.8123	$116.81	$116.80	$116.80
Purchase #3	$147.44	6.331%	$156.7744	$156.77	$156.75	$156.80
Purchase #4	$194.96	8.541%	$211.6115	$211.61	$211.60	$211.60
Purchase #5	$99.70	10.164%	$109.8335	$109.83	$109.85	$109.80
Purchase #6	$64.42	3.446%	$66.6399	$66.64	$66.65	$66.60
Purchase #7	$190.40	4.645%	$199.2441	$199.24	$199.25	$199.20
7 purchase totals =	$972.33		$1,048.2266	$1,048.21	$1,048.20	$1,048.10