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	$64.42	5.264%	$67.8111	$67.81	$67.80	$67.80
Purchase #2	$213.31	11.630%	$238.118	$238.12	$238.10	$238.10
Purchase #3	$37.39	11.432%	$41.6644	$41.66	$41.65	$41.70
Purchase #4	$23.36	10.763%	$25.8742	$25.87	$25.85	$25.90
Purchase #5	$103.63	5.399%	$109.225	$109.23	$109.25	$109.20
Purchase #6	$88.28	7.752%	$95.1235	$95.12	$95.10	$95.10
Purchase #7	$40.28	13.598%	$45.7573	$45.76	$45.75	$45.80
7 purchase totals =	$570.67		$623.5735	$623.57	$623.50	$623.60