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	$67.78	3.510%	$70.1591	$70.16	$70.15	$70.20
Purchase #2	$248.45	13.317%	$281.5361	$281.54	$281.55	$281.50
Purchase #3	$155.88	3.210%	$160.8837	$160.88	$160.90	$160.90
Purchase #4	$233.50	8.505%	$253.3592	$253.36	$253.35	$253.40
Purchase #5	$52.49	11.571%	$58.5636	$58.56	$58.55	$58.60
Purchase #6	$87.88	13.259%	$99.532	$99.53	$99.55	$99.50
Purchase #7	$137.33	10.846%	$152.2248	$152.22	$152.20	$152.20
7 purchase totals =	$983.31		$1,076.2585	$1,076.25	$1,076.25	$1,076.30