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	$239.66	6.602%	$255.4824	$255.48	$255.50	$255.50
Purchase #2	$28.33	7.113%	$30.3451	$30.35	$30.35	$30.30
Purchase #3	$45.37	7.514%	$48.7791	$48.78	$48.80	$48.80
Purchase #4	$22.64	13.853%	$25.7763	$25.78	$25.80	$25.80
Purchase #5	$44.34	7.514%	$47.6717	$47.67	$47.65	$47.70
Purchase #6	$35.72	5.173%	$37.5678	$37.57	$37.55	$37.60
Purchase #7	$171.96	7.717%	$185.2302	$185.23	$185.25	$185.20
7 purchase totals =	$588.02		$630.8526	$630.86	$630.90	$630.90