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	$24.50	11.299%	$27.2683	$27.27	$27.25	$27.30
Purchase #2	$130.63	9.355%	$142.8504	$142.85	$142.85	$142.90
Purchase #3	$242.73	8.134%	$262.4737	$262.47	$262.45	$262.50
Purchase #4	$37.69	10.248%	$41.5525	$41.55	$41.55	$41.60
Purchase #5	$145.74	13.802%	$165.855	$165.86	$165.85	$165.90
Purchase #6	$109.82	8.702%	$119.3765	$119.38	$119.40	$119.40
Purchase #7	$72.48	7.754%	$78.1001	$78.10	$78.10	$78.10
7 purchase totals =	$763.59		$837.4765	$837.48	$837.45	$837.70