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	$52.61	5.214%	$55.3531	$55.35	$55.35	$55.40
Purchase #2	$29.56	4.810%	$30.9818	$30.98	$31.00	$31.00
Purchase #3	$187.34	8.650%	$203.5449	$203.54	$203.55	$203.50
Purchase #4	$129.32	12.816%	$145.8937	$145.89	$145.90	$145.90
Purchase #5	$162.45	4.252%	$169.3574	$169.36	$169.35	$169.40
Purchase #6	$249.36	5.610%	$263.3491	$263.35	$263.35	$263.30
Purchase #7	$134.37	4.123%	$139.9101	$139.91	$139.90	$139.90
7 purchase totals =	$945.01		$1,008.3901	$1,008.38	$1,008.40	$1,008.40