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	$67.60	5.152%	$71.0828	$71.08	$71.10	$71.10
Purchase #2	$46.42	8.518%	$50.3741	$50.37	$50.35	$50.40
Purchase #3	$169.38	3.854%	$175.9079	$175.91	$175.90	$175.90
Purchase #4	$233.55	11.740%	$260.9688	$260.97	$260.95	$261.00
Purchase #5	$20.59	4.117%	$21.4377	$21.44	$21.45	$21.40
Purchase #6	$104.56	11.874%	$116.9755	$116.98	$117.00	$117.00
Purchase #7	$123.66	13.310%	$140.1191	$140.12	$140.10	$140.10
7 purchase totals =	$765.76		$836.8659	$836.87	$836.85	$836.90