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	$96.51	3.453%	$99.8425	$99.84	$99.85	$99.80
Purchase #2	$83.27	3.129%	$85.8755	$85.88	$85.90	$85.90
Purchase #3	$246.60	7.322%	$264.6561	$264.66	$264.65	$264.70
Purchase #4	$167.71	12.610%	$188.8582	$188.86	$188.85	$188.90
Purchase #5	$176.65	13.360%	$200.2504	$200.25	$200.25	$200.30
Purchase #6	$81.65	10.327%	$90.082	$90.08	$90.10	$90.10
Purchase #7	$53.71	13.504%	$60.963	$60.96	$60.95	$61.00
7 purchase totals =	$906.10		$990.5277	$990.53	$990.55	$990.70