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	$100.46	3.769%	$104.2463	$104.25	$104.25	$104.20
Purchase #2	$134.36	11.538%	$149.8625	$149.86	$149.85	$149.90
Purchase #3	$234.49	11.626%	$261.7518	$261.75	$261.75	$261.80
Purchase #4	$246.47	11.712%	$275.3366	$275.34	$275.35	$275.30
Purchase #5	$123.56	12.825%	$139.4066	$139.41	$139.40	$139.40
Purchase #6	$186.36	5.380%	$196.3862	$196.39	$196.40	$196.40
Purchase #7	$52.81	4.305%	$55.0835	$55.08	$55.10	$55.10
7 purchase totals =	$1,078.51		$1,182.0735	$1,182.08	$1,182.10	$1,182.10