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	$37.27	8.859%	$40.5717	$40.57	$40.55	$40.60
Purchase #2	$167.77	13.142%	$189.8183	$189.82	$189.80	$189.80
Purchase #3	$171.71	11.296%	$191.1064	$191.11	$191.10	$191.10
Purchase #4	$43.83	11.516%	$48.8775	$48.88	$48.90	$48.90
Purchase #5	$243.53	7.287%	$261.276	$261.28	$261.30	$261.30
Purchase #6	$250.73	8.734%	$272.6288	$272.63	$272.65	$272.60
Purchase #7	$162.75	3.856%	$169.0256	$169.03	$169.05	$169.00
7 purchase totals =	$1,077.59		$1,173.3043	$1,173.32	$1,173.35	$1,173.30