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	$191.33	12.701%	$215.6308	$215.63	$215.65	$215.60
Purchase #2	$216.89	8.600%	$235.5425	$235.54	$235.55	$235.50
Purchase #3	$37.87	10.356%	$41.7918	$41.79	$41.80	$41.80
Purchase #4	$110.89	6.342%	$117.9226	$117.92	$117.90	$117.90
Purchase #5	$172.77	10.464%	$190.8487	$190.85	$190.85	$190.80
Purchase #6	$57.79	3.481%	$59.8017	$59.80	$59.80	$59.80
Purchase #7	$54.97	13.854%	$62.5855	$62.59	$62.60	$62.60
7 purchase totals =	$842.51		$924.1236	$924.12	$924.15	$924.00