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	$126.27	10.325%	$139.3074	$139.31	$139.30	$139.30
Purchase #2	$52.75	10.503%	$58.2903	$58.29	$58.30	$58.30
Purchase #3	$124.77	12.399%	$140.2402	$140.24	$140.25	$140.20
Purchase #4	$65.85	10.745%	$72.9256	$72.93	$72.95	$72.90
Purchase #5	$131.40	3.865%	$136.4786	$136.48	$136.50	$136.50
Purchase #6	$93.71	7.274%	$100.5265	$100.53	$100.55	$100.50
Purchase #7	$58.49	8.683%	$63.5687	$63.57	$63.55	$63.60
7 purchase totals =	$653.24		$711.3373	$711.35	$711.40	$711.30