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	$117.34	12.561%	$132.0791	$132.08	$132.10	$132.10
Purchase #2	$104.89	5.462%	$110.6191	$110.62	$110.60	$110.60
Purchase #3	$165.34	8.402%	$179.2319	$179.23	$179.25	$179.20
Purchase #4	$57.42	9.740%	$63.0127	$63.01	$63.00	$63.00
Purchase #5	$208.48	10.268%	$229.8867	$229.89	$229.90	$229.90
Purchase #6	$203.47	7.739%	$219.2165	$219.22	$219.20	$219.20
Purchase #7	$69.77	12.274%	$78.3336	$78.33	$78.35	$78.30
7 purchase totals =	$926.71		$1,012.3796	$1,012.38	$1,012.40	$1,012.30