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	$220.87	12.785%	$249.1082	$249.11	$249.10	$249.10
Purchase #2	$13.51	12.282%	$15.1693	$15.17	$15.15	$15.20
Purchase #3	$170.50	5.870%	$180.5084	$180.51	$180.50	$180.50
Purchase #4	$179.32	11.725%	$200.3453	$200.35	$200.35	$200.30
Purchase #5	$189.72	9.693%	$208.1096	$208.11	$208.10	$208.10
Purchase #6	$215.44	4.593%	$225.3352	$225.34	$225.35	$225.30
Purchase #7	$102.82	9.822%	$112.919	$112.92	$112.90	$112.90
7 purchase totals =	$1,092.18		$1,191.4950	$1,191.51	$1,191.45	$1,191.40