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	$71.54	9.360%	$78.2361	$78.24	$78.25	$78.20
Purchase #2	$90.53	9.705%	$99.3159	$99.32	$99.30	$99.30
Purchase #3	$37.71	5.514%	$39.7893	$39.79	$39.80	$39.80
Purchase #4	$198.40	4.793%	$207.9093	$207.91	$207.90	$207.90
Purchase #5	$226.87	10.256%	$250.1378	$250.14	$250.15	$250.10
Purchase #6	$71.43	8.105%	$77.2194	$77.22	$77.20	$77.20
Purchase #7	$50.32	9.814%	$55.2584	$55.26	$55.25	$55.30
7 purchase totals =	$746.80		$807.8662	$807.88	$807.85	$807.80