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	$101.90	13.626%	$115.7849	$115.78	$115.80	$115.80
Purchase #2	$59.37	8.742%	$64.5601	$64.56	$64.55	$64.60
Purchase #3	$11.43	9.162%	$12.4772	$12.48	$12.50	$12.50
Purchase #4	$85.94	3.586%	$89.0218	$89.02	$89.00	$89.00
Purchase #5	$64.44	5.302%	$67.8566	$67.86	$67.85	$67.90
Purchase #6	$249.57	13.534%	$283.3468	$283.35	$283.35	$283.30
Purchase #7	$53.87	12.705%	$60.7142	$60.71	$60.70	$60.70
7 purchase totals =	$626.52		$693.7616	$693.76	$693.75	$693.80