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	$56.77	3.681%	$58.8597	$58.86	$58.85	$58.90
Purchase #2	$148.70	11.390%	$165.6369	$165.64	$165.65	$165.60
Purchase #3	$74.83	9.801%	$82.1641	$82.16	$82.15	$82.20
Purchase #4	$118.29	8.596%	$128.4582	$128.46	$128.45	$128.50
Purchase #5	$104.34	12.851%	$117.7487	$117.75	$117.75	$117.70
Purchase #6	$45.39	11.407%	$50.5676	$50.57	$50.55	$50.60
Purchase #7	$169.46	6.780%	$180.9494	$180.95	$180.95	$180.90
7 purchase totals =	$717.78		$784.3846	$784.39	$784.35	$784.40