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	$42.56	12.233%	$47.7664	$47.77	$47.75	$47.80
Purchase #2	$54.92	4.214%	$57.2343	$57.23	$57.25	$57.20
Purchase #3	$166.35	9.349%	$181.9021	$181.90	$181.90	$181.90
Purchase #4	$209.75	9.331%	$229.3218	$229.32	$229.30	$229.30
Purchase #5	$45.89	7.358%	$49.2666	$49.27	$49.25	$49.30
Purchase #6	$226.89	10.460%	$250.6227	$250.62	$250.60	$250.60
Purchase #7	$152.39	10.603%	$168.5479	$168.55	$168.55	$168.50
7 purchase totals =	$898.75		$984.6618	$984.66	$984.60	$984.60