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	$91.71	11.576%	$102.3263	$102.33	$102.35	$102.30
Purchase #2	$33.58	12.700%	$37.8447	$37.84	$37.85	$37.80
Purchase #3	$220.56	9.433%	$241.3654	$241.37	$241.35	$241.40
Purchase #4	$42.91	9.481%	$46.9783	$46.98	$47.00	$47.00
Purchase #5	$63.86	12.463%	$71.8189	$71.82	$71.80	$71.80
Purchase #6	$16.95	5.126%	$17.8189	$17.82	$17.80	$17.80
Purchase #7	$83.96	6.754%	$89.6307	$89.63	$89.65	$89.60
7 purchase totals =	$553.53		$607.7832	$607.79	$607.80	$607.70