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	$83.60	8.105%	$90.3758	$90.38	$90.40	$90.40
Purchase #2	$63.73	9.814%	$69.9845	$69.98	$70.00	$70.00
Purchase #3	$83.62	4.509%	$87.3904	$87.39	$87.40	$87.40
Purchase #4	$147.88	12.188%	$165.9036	$165.90	$165.90	$165.90
Purchase #5	$49.83	10.279%	$54.952	$54.95	$54.95	$55.00
Purchase #6	$75.27	12.765%	$84.8782	$84.88	$84.90	$84.90
Purchase #7	$247.46	8.437%	$268.3382	$268.34	$268.35	$268.30
7 purchase totals =	$751.39		$821.8227	$821.82	$821.90	$821.90