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	$115.48	7.192%	$123.7853	$123.79	$123.80	$123.80
Purchase #2	$172.90	10.675%	$191.3571	$191.36	$191.35	$191.40
Purchase #3	$74.45	12.679%	$83.8895	$83.89	$83.90	$83.90
Purchase #4	$128.39	10.494%	$141.8632	$141.86	$141.85	$141.90
Purchase #5	$155.55	7.536%	$167.2722	$167.27	$167.25	$167.30
Purchase #6	$79.73	6.776%	$85.1325	$85.13	$85.15	$85.10
Purchase #7	$131.85	12.613%	$148.4802	$148.48	$148.50	$148.50
7 purchase totals =	$858.35		$941.7800	$941.78	$941.80	$941.90