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	$141.26	9.131%	$154.1585	$154.16	$154.15	$154.20
Purchase #2	$35.36	11.115%	$39.2903	$39.29	$39.30	$39.30
Purchase #3	$79.73	3.470%	$82.4966	$82.50	$82.50	$82.50
Purchase #4	$220.42	13.520%	$250.2208	$250.22	$250.20	$250.20
Purchase #5	$82.93	9.576%	$90.8714	$90.87	$90.85	$90.90
Purchase #6	$78.73	12.227%	$88.3563	$88.36	$88.35	$88.40
Purchase #7	$218.27	5.870%	$231.0824	$231.08	$231.10	$231.10
7 purchase totals =	$856.70		$936.4763	$936.48	$936.45	$936.60