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	$78.63	5.456%	$82.9201	$82.92	$82.90	$82.90
Purchase #2	$199.80	11.501%	$222.779	$222.78	$222.80	$222.80
Purchase #3	$60.95	7.259%	$65.3744	$65.37	$65.35	$65.40
Purchase #4	$165.90	13.623%	$188.5006	$188.50	$188.50	$188.50
Purchase #5	$29.73	12.166%	$33.347	$33.35	$33.35	$33.30
Purchase #6	$207.57	13.138%	$234.8405	$234.84	$234.85	$234.80
Purchase #7	$33.57	7.165%	$35.9753	$35.98	$36.00	$36.00
7 purchase totals =	$776.15		$863.7369	$863.74	$863.75	$863.70