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	$38.45	11.666%	$42.9356	$42.94	$42.95	$42.90
Purchase #2	$191.76	9.688%	$210.3377	$210.34	$210.35	$210.30
Purchase #3	$167.48	11.489%	$186.7218	$186.72	$186.70	$186.70
Purchase #4	$229.43	12.659%	$258.4735	$258.47	$258.45	$258.50
Purchase #5	$238.45	11.179%	$265.1063	$265.11	$265.10	$265.10
Purchase #6	$210.57	8.864%	$229.2349	$229.23	$229.25	$229.20
Purchase #7	$107.66	4.463%	$112.4649	$112.46	$112.45	$112.50
7 purchase totals =	$1,183.80		$1,305.2747	$1,305.27	$1,305.25	$1,305.20