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	$123.34	13.814%	$140.3782	$140.38	$140.40	$140.40
Purchase #2	$9.73	13.310%	$11.0251	$11.03	$11.05	$11.00
Purchase #3	$188.62	4.364%	$196.8514	$196.85	$196.85	$196.90
Purchase #4	$44.77	5.843%	$47.3859	$47.39	$47.40	$47.40
Purchase #5	$174.70	12.712%	$196.9079	$196.91	$196.90	$196.90
Purchase #6	$50.41	9.269%	$55.0825	$55.08	$55.10	$55.10
Purchase #7	$15.53	11.804%	$17.3632	$17.36	$17.35	$17.40
7 purchase totals =	$607.10		$664.9942	$665.00	$665.05	$665.10