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	$81.97	12.112%	$91.8982	$91.90	$91.90	$91.90
Purchase #2	$149.26	12.475%	$167.8802	$167.88	$167.90	$167.90
Purchase #3	$10.44	12.513%	$11.7464	$11.75	$11.75	$11.70
Purchase #4	$162.61	6.156%	$172.6203	$172.62	$172.60	$172.60
Purchase #5	$38.66	13.351%	$43.8215	$43.82	$43.80	$43.80
Purchase #6	$88.63	11.787%	$99.0768	$99.08	$99.10	$99.10
Purchase #7	$221.86	5.818%	$234.7678	$234.77	$234.75	$234.80
7 purchase totals =	$753.43		$821.8112	$821.82	$821.80	$821.80