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	$47.90	3.303%	$49.4821	$49.48	$49.50	$49.50
Purchase #2	$197.83	10.454%	$218.5111	$218.51	$218.50	$218.50
Purchase #3	$85.40	3.648%	$88.5154	$88.52	$88.50	$88.50
Purchase #4	$211.89	8.428%	$229.7481	$229.75	$229.75	$229.70
Purchase #5	$132.97	12.859%	$150.0686	$150.07	$150.05	$150.10
Purchase #6	$104.96	10.732%	$116.2243	$116.22	$116.20	$116.20
Purchase #7	$106.88	9.836%	$117.3927	$117.39	$117.40	$117.40
7 purchase totals =	$887.83		$969.9423	$969.94	$969.90	$969.90