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	$221.71	12.369%	$249.1333	$249.13	$249.15	$249.10
Purchase #2	$7.72	5.405%	$8.1373	$8.14	$8.15	$8.10
Purchase #3	$119.98	6.421%	$127.6839	$127.68	$127.70	$127.70
Purchase #4	$152.32	10.222%	$167.8902	$167.89	$167.90	$167.90
Purchase #5	$76.38	7.865%	$82.3873	$82.39	$82.40	$82.40
Purchase #6	$109.89	6.644%	$117.1911	$117.19	$117.20	$117.20
Purchase #7	$24.55	13.112%	$27.769	$27.77	$27.75	$27.80
7 purchase totals =	$712.55		$780.1921	$780.19	$780.25	$780.20