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	$129.66	5.299%	$136.5307	$136.53	$136.55	$136.50
Purchase #2	$94.35	6.677%	$100.6497	$100.65	$100.65	$100.60
Purchase #3	$58.27	7.317%	$62.5336	$62.53	$62.55	$62.50
Purchase #4	$150.56	11.222%	$167.4558	$167.46	$167.45	$167.50
Purchase #5	$79.48	12.249%	$89.2155	$89.22	$89.20	$89.20
Purchase #6	$206.97	4.762%	$216.8259	$216.83	$216.85	$216.80
Purchase #7	$201.45	9.338%	$220.2614	$220.26	$220.25	$220.30
7 purchase totals =	$920.74		$993.4726	$993.48	$993.50	$993.40