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	$134.93	3.616%	$139.8091	$139.81	$139.80	$139.80
Purchase #2	$94.51	11.246%	$105.1386	$105.14	$105.15	$105.10
Purchase #3	$216.62	12.298%	$243.2599	$243.26	$243.25	$243.30
Purchase #4	$127.46	10.276%	$140.5578	$140.56	$140.55	$140.60
Purchase #5	$162.95	3.167%	$168.1106	$168.11	$168.10	$168.10
Purchase #6	$123.31	13.804%	$140.3317	$140.33	$140.35	$140.30
Purchase #7	$24.44	11.136%	$27.1616	$27.16	$27.15	$27.20
7 purchase totals =	$884.22		$964.3693	$964.37	$964.35	$964.40