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	$102.61	6.655%	$109.4387	$109.44	$109.45	$109.40
Purchase #2	$64.88	10.292%	$71.5574	$71.56	$71.55	$71.60
Purchase #3	$9.76	8.184%	$10.5588	$10.56	$10.55	$10.60
Purchase #4	$234.94	6.316%	$249.7788	$249.78	$249.80	$249.80
Purchase #5	$52.67	12.871%	$59.4492	$59.45	$59.45	$59.40
Purchase #6	$24.26	13.143%	$27.4485	$27.45	$27.45	$27.40
Purchase #7	$101.48	13.328%	$115.0053	$115.01	$115.00	$115.00
7 purchase totals =	$590.60		$643.2367	$643.25	$643.25	$643.20