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	$85.41	6.434%	$90.9053	$90.91	$90.90	$90.90
Purchase #2	$65.26	3.133%	$67.3046	$67.30	$67.30	$67.30
Purchase #3	$127.36	10.276%	$140.4475	$140.45	$140.45	$140.40
Purchase #4	$173.94	6.111%	$184.5695	$184.57	$184.55	$184.60
Purchase #5	$36.35	4.395%	$37.9476	$37.95	$37.95	$37.90
Purchase #6	$220.63	3.698%	$228.7889	$228.79	$228.80	$228.80
Purchase #7	$88.44	9.310%	$96.6738	$96.67	$96.65	$96.70
7 purchase totals =	$797.39		$846.6372	$846.64	$846.60	$846.60