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	$31.68	4.442%	$33.0872	$33.09	$33.10	$33.10
Purchase #2	$119.50	11.787%	$133.5855	$133.59	$133.60	$133.60
Purchase #3	$94.51	6.199%	$100.3687	$100.37	$100.35	$100.40
Purchase #4	$125.31	10.584%	$138.5728	$138.57	$138.55	$138.60
Purchase #5	$89.31	12.505%	$100.4782	$100.48	$100.50	$100.50
Purchase #6	$166.49	12.391%	$187.1198	$187.12	$187.10	$187.10
Purchase #7	$66.57	4.538%	$69.5909	$69.59	$69.60	$69.60
7 purchase totals =	$693.37		$762.8031	$762.81	$762.80	$762.90