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	$12.53	3.616%	$12.9831	$12.98	$13.00	$13.00
Purchase #2	$34.80	7.636%	$37.4573	$37.46	$37.45	$37.50
Purchase #3	$243.27	4.218%	$253.5311	$253.53	$253.55	$253.50
Purchase #4	$160.48	7.516%	$172.5417	$172.54	$172.55	$172.50
Purchase #5	$29.33	3.339%	$30.3093	$30.31	$30.30	$30.30
Purchase #6	$62.26	12.690%	$70.1608	$70.16	$70.15	$70.20
Purchase #7	$106.59	9.661%	$116.8877	$116.89	$116.90	$116.90
7 purchase totals =	$649.26		$693.8710	$693.87	$693.90	$693.90