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	$132.71	10.401%	$146.5132	$146.51	$146.50	$146.50
Purchase #2	$249.33	12.258%	$279.8929	$279.89	$279.90	$279.90
Purchase #3	$85.75	12.282%	$96.2818	$96.28	$96.30	$96.30
Purchase #4	$76.88	11.166%	$85.4644	$85.46	$85.45	$85.50
Purchase #5	$112.91	13.687%	$128.364	$128.36	$128.35	$128.40
Purchase #6	$40.57	13.106%	$45.8871	$45.89	$45.90	$45.90
Purchase #7	$90.98	6.114%	$96.5425	$96.54	$96.55	$96.50
7 purchase totals =	$789.13		$878.9459	$878.93	$878.95	$879.00