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	$89.52	3.767%	$92.8922	$92.89	$92.90	$92.90
Purchase #2	$56.77	11.221%	$63.1402	$63.14	$63.15	$63.10
Purchase #3	$94.28	8.590%	$102.3787	$102.38	$102.40	$102.40
Purchase #4	$209.65	8.614%	$227.7093	$227.71	$227.70	$227.70
Purchase #5	$92.83	4.105%	$96.6407	$96.64	$96.65	$96.60
Purchase #6	$86.47	11.463%	$96.3821	$96.38	$96.40	$96.40
Purchase #7	$89.78	13.696%	$102.0763	$102.08	$102.10	$102.10
7 purchase totals =	$719.30		$781.2195	$781.22	$781.30	$781.20