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	$113.91	6.363%	$121.1581	$121.16	$121.15	$121.20
Purchase #2	$112.78	3.141%	$116.3224	$116.32	$116.30	$116.30
Purchase #3	$81.36	10.282%	$89.7254	$89.73	$89.75	$89.70
Purchase #4	$186.56	4.581%	$195.1063	$195.11	$195.10	$195.10
Purchase #5	$77.98	6.228%	$82.8366	$82.84	$82.85	$82.80
Purchase #6	$81.49	9.396%	$89.1468	$89.15	$89.15	$89.10
Purchase #7	$54.77	7.328%	$58.7835	$58.78	$58.80	$58.80
7 purchase totals =	$708.85		$753.0791	$753.09	$753.10	$753.00