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	$121.86	12.319%	$136.8719	$136.87	$136.85	$136.90
Purchase #2	$119.66	7.649%	$128.8128	$128.81	$128.80	$128.80
Purchase #3	$249.95	11.184%	$277.9044	$277.90	$277.90	$277.90
Purchase #4	$52.95	12.217%	$59.4189	$59.42	$59.40	$59.40
Purchase #5	$77.27	10.803%	$85.6175	$85.62	$85.60	$85.60
Purchase #6	$68.35	10.497%	$75.5247	$75.52	$75.50	$75.50
Purchase #7	$55.53	13.192%	$62.8555	$62.86	$62.85	$62.90
7 purchase totals =	$745.57		$827.0057	$827.00	$826.90	$827.00