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	$95.88	4.113%	$99.8235	$99.82	$99.80	$99.80
Purchase #2	$159.49	3.303%	$164.758	$164.76	$164.75	$164.80
Purchase #3	$134.95	12.818%	$152.2479	$152.25	$152.25	$152.20
Purchase #4	$49.38	8.655%	$53.6538	$53.65	$53.65	$53.70
Purchase #5	$160.71	12.644%	$181.0302	$181.03	$181.05	$181.00
Purchase #6	$21.92	13.427%	$24.8632	$24.86	$24.85	$24.90
Purchase #7	$250.56	8.135%	$270.9431	$270.94	$270.95	$270.90
7 purchase totals =	$872.89		$947.3197	$947.31	$947.30	$947.30