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	$96.37	13.432%	$109.3144	$109.31	$109.30	$109.30
Purchase #2	$247.82	6.597%	$264.1687	$264.17	$264.15	$264.20
Purchase #3	$148.69	6.380%	$158.1764	$158.18	$158.20	$158.20
Purchase #4	$40.98	8.545%	$44.4817	$44.48	$44.50	$44.50
Purchase #5	$65.55	8.788%	$71.3105	$71.31	$71.30	$71.30
Purchase #6	$135.34	11.391%	$150.7566	$150.76	$150.75	$150.80
Purchase #7	$68.82	3.775%	$71.418	$71.42	$71.40	$71.40
7 purchase totals =	$803.57		$869.6263	$869.63	$869.60	$869.70