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	$218.46	6.745%	$233.1951	$233.20	$233.20	$233.20
Purchase #2	$116.74	12.360%	$131.1691	$131.17	$131.15	$131.20
Purchase #3	$210.75	5.683%	$222.7269	$222.73	$222.75	$222.70
Purchase #4	$37.73	13.604%	$42.8628	$42.86	$42.85	$42.90
Purchase #5	$161.83	6.229%	$171.9104	$171.91	$171.90	$171.90
Purchase #6	$33.35	3.290%	$34.4472	$34.45	$34.45	$34.40
Purchase #7	$125.69	6.203%	$133.4866	$133.49	$133.50	$133.50
7 purchase totals =	$904.55		$969.7981	$969.81	$969.80	$969.80