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	$59.38	9.711%	$65.1464	$65.15	$65.15	$65.10
Purchase #2	$52.80	13.802%	$60.0875	$60.09	$60.10	$60.10
Purchase #3	$36.95	10.734%	$40.9162	$40.92	$40.90	$40.90
Purchase #4	$155.49	4.545%	$162.557	$162.56	$162.55	$162.60
Purchase #5	$82.91	12.756%	$93.486	$93.49	$93.50	$93.50
Purchase #6	$11.98	12.757%	$13.5083	$13.51	$13.50	$13.50
Purchase #7	$100.79	5.360%	$106.1923	$106.19	$106.20	$106.20
7 purchase totals =	$500.30		$541.8937	$541.91	$541.90	$541.90