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	$56.98	6.548%	$60.7111	$60.71	$60.70	$60.70
Purchase #2	$146.56	8.715%	$159.3327	$159.33	$159.35	$159.30
Purchase #3	$118.51	4.185%	$123.4696	$123.47	$123.45	$123.50
Purchase #4	$90.33	7.350%	$96.9693	$96.97	$96.95	$97.00
Purchase #5	$32.82	11.288%	$36.5247	$36.52	$36.50	$36.50
Purchase #6	$217.46	4.636%	$227.5414	$227.54	$227.55	$227.50
Purchase #7	$78.33	12.701%	$88.2787	$88.28	$88.30	$88.30
7 purchase totals =	$740.99		$792.8275	$792.82	$792.80	$792.80