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	$72.58	6.243%	$77.1112	$77.11	$77.10	$77.10
Purchase #2	$192.84	13.144%	$218.1869	$218.19	$218.20	$218.20
Purchase #3	$130.41	7.267%	$139.8869	$139.89	$139.90	$139.90
Purchase #4	$236.98	10.709%	$262.3582	$262.36	$262.35	$262.40
Purchase #5	$169.48	7.298%	$181.8487	$181.85	$181.85	$181.80
Purchase #6	$123.32	11.280%	$137.2305	$137.23	$137.25	$137.20
Purchase #7	$66.47	9.220%	$72.5985	$72.60	$72.60	$72.60
7 purchase totals =	$992.08		$1,089.2209	$1,089.23	$1,089.25	$1,089.20