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	$98.56	3.601%	$102.1091	$102.11	$102.10	$102.10
Purchase #2	$249.57	12.307%	$280.2846	$280.28	$280.30	$280.30
Purchase #3	$98.71	11.292%	$109.8563	$109.86	$109.85	$109.90
Purchase #4	$224.71	5.496%	$237.0601	$237.06	$237.05	$237.10
Purchase #5	$108.95	4.483%	$113.8342	$113.83	$113.85	$113.80
Purchase #6	$116.27	11.772%	$129.9573	$129.96	$129.95	$130.00
Purchase #7	$26.99	10.319%	$29.7751	$29.78	$29.80	$29.80
7 purchase totals =	$923.76		$1,002.8767	$1,002.88	$1,002.90	$1,003.00