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	$51.63	9.607%	$56.5901	$56.59	$56.60	$56.60
Purchase #2	$66.74	9.191%	$72.8741	$72.87	$72.85	$72.90
Purchase #3	$33.97	4.132%	$35.3736	$35.37	$35.35	$35.40
Purchase #4	$228.73	8.246%	$247.5911	$247.59	$247.60	$247.60
Purchase #5	$185.27	6.319%	$196.9772	$196.98	$197.00	$197.00
Purchase #6	$218.82	12.868%	$246.9778	$246.98	$247.00	$247.00
Purchase #7	$62.62	7.673%	$67.4248	$67.42	$67.40	$67.40
7 purchase totals =	$847.78		$923.8087	$923.80	$923.80	$923.90