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	$94.30	5.369%	$99.363	$99.36	$99.35	$99.40
Purchase #2	$61.28	9.279%	$66.9662	$66.97	$66.95	$67.00
Purchase #3	$208.34	12.115%	$233.5804	$233.58	$233.60	$233.60
Purchase #4	$58.75	11.355%	$65.4211	$65.42	$65.40	$65.40
Purchase #5	$28.91	13.732%	$32.8799	$32.88	$32.90	$32.90
Purchase #6	$78.42	5.844%	$83.0029	$83.00	$83.00	$83.00
Purchase #7	$86.56	10.785%	$95.8955	$95.90	$95.90	$95.90
7 purchase totals =	$616.56		$677.1090	$677.11	$677.10	$677.20