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	$54.51	6.357%	$57.9752	$57.98	$58.00	$58.00
Purchase #2	$82.33	11.653%	$91.9239	$91.92	$91.90	$91.90
Purchase #3	$187.27	11.651%	$209.0888	$209.09	$209.10	$209.10
Purchase #4	$203.68	5.743%	$215.3773	$215.38	$215.40	$215.40
Purchase #5	$55.49	6.517%	$59.1063	$59.11	$59.10	$59.10
Purchase #6	$57.75	3.103%	$59.542	$59.54	$59.55	$59.50
Purchase #7	$101.59	7.611%	$109.322	$109.32	$109.30	$109.30
7 purchase totals =	$742.62		$802.3355	$802.34	$802.35	$802.30