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	$23.81	7.254%	$25.5372	$25.54	$25.55	$25.50
Purchase #2	$157.77	3.192%	$162.806	$162.81	$162.80	$162.80
Purchase #3	$109.69	11.645%	$122.4634	$122.46	$122.45	$122.50
Purchase #4	$37.52	7.704%	$40.4105	$40.41	$40.40	$40.40
Purchase #5	$70.51	12.328%	$79.2025	$79.20	$79.20	$79.20
Purchase #6	$207.72	7.119%	$222.5076	$222.51	$222.50	$222.50
Purchase #7	$101.71	11.342%	$113.2459	$113.25	$113.25	$113.20
7 purchase totals =	$708.73		$766.1731	$766.18	$766.15	$766.10