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	$76.41	3.151%	$78.8177	$78.82	$78.80	$78.80
Purchase #2	$139.90	13.470%	$158.7445	$158.74	$158.75	$158.70
Purchase #3	$82.36	10.443%	$90.9609	$90.96	$90.95	$91.00
Purchase #4	$207.93	3.612%	$215.4404	$215.44	$215.45	$215.40
Purchase #5	$90.98	10.441%	$100.4792	$100.48	$100.50	$100.50
Purchase #6	$64.65	4.460%	$67.5334	$67.53	$67.55	$67.50
Purchase #7	$177.89	13.762%	$202.3712	$202.37	$202.35	$202.40
7 purchase totals =	$840.12		$914.3473	$914.34	$914.35	$914.30