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	$66.64	8.527%	$72.3224	$72.32	$72.30	$72.30
Purchase #2	$188.65	12.334%	$211.9181	$211.92	$211.90	$211.90
Purchase #3	$98.41	4.196%	$102.5393	$102.54	$102.55	$102.50
Purchase #4	$135.38	10.788%	$149.9848	$149.98	$150.00	$150.00
Purchase #5	$86.74	13.623%	$98.5566	$98.56	$98.55	$98.60
Purchase #6	$86.48	4.173%	$90.0888	$90.09	$90.10	$90.10
Purchase #7	$7.93	7.496%	$8.5244	$8.52	$8.50	$8.50
7 purchase totals =	$670.23		$733.9344	$733.93	$733.90	$733.90