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	$44.36	11.503%	$49.4627	$49.46	$49.45	$49.50
Purchase #2	$41.69	3.628%	$43.2025	$43.20	$43.20	$43.20
Purchase #3	$162.33	10.552%	$179.4591	$179.46	$179.45	$179.50
Purchase #4	$167.67	10.642%	$185.5134	$185.51	$185.50	$185.50
Purchase #5	$13.28	3.407%	$13.7324	$13.73	$13.75	$13.70
Purchase #6	$224.25	9.403%	$245.3362	$245.34	$245.35	$245.30
Purchase #7	$210.35	10.849%	$233.1709	$233.17	$233.15	$233.20
7 purchase totals =	$863.93		$949.8772	$949.87	$949.85	$949.90