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	$99.61	6.686%	$106.2699	$106.27	$106.25	$106.30
Purchase #2	$220.86	8.798%	$240.2913	$240.29	$240.30	$240.30
Purchase #3	$19.80	8.617%	$21.5062	$21.51	$21.50	$21.50
Purchase #4	$37.90	10.163%	$41.7518	$41.75	$41.75	$41.80
Purchase #5	$86.30	11.413%	$96.1494	$96.15	$96.15	$96.10
Purchase #6	$54.54	5.508%	$57.5441	$57.54	$57.55	$57.50
Purchase #7	$232.72	7.807%	$250.8885	$250.89	$250.90	$250.90
7 purchase totals =	$751.73		$814.4012	$814.40	$814.40	$814.40