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	$85.67	13.796%	$97.489	$97.49	$97.50	$97.50
Purchase #2	$58.91	3.573%	$61.0149	$61.01	$61.00	$61.00
Purchase #3	$171.30	11.398%	$190.8248	$190.82	$190.80	$190.80
Purchase #4	$43.71	3.289%	$45.1476	$45.15	$45.15	$45.10
Purchase #5	$29.42	5.278%	$30.9728	$30.97	$30.95	$31.00
Purchase #6	$18.55	11.284%	$20.6432	$20.64	$20.65	$20.60
Purchase #7	$102.56	7.188%	$109.932	$109.93	$109.95	$109.90
7 purchase totals =	$510.12		$556.0243	$556.01	$556.00	$555.90