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	$38.61	9.183%	$42.1556	$42.16	$42.15	$42.20
Purchase #2	$235.68	3.490%	$243.9052	$243.91	$243.90	$243.90
Purchase #3	$51.98	9.468%	$56.9015	$56.90	$56.90	$56.90
Purchase #4	$97.56	6.500%	$103.9014	$103.90	$103.90	$103.90
Purchase #5	$119.39	8.312%	$129.3137	$129.31	$129.30	$129.30
Purchase #6	$76.27	11.571%	$85.0952	$85.10	$85.10	$85.10
Purchase #7	$81.97	10.146%	$90.2867	$90.29	$90.30	$90.30
7 purchase totals =	$701.46		$751.5593	$751.57	$751.55	$751.60