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	$37.96	12.185%	$42.5854	$42.59	$42.60	$42.60
Purchase #2	$208.93	12.136%	$234.2857	$234.29	$234.30	$234.30
Purchase #3	$50.89	10.555%	$56.2614	$56.26	$56.25	$56.30
Purchase #4	$249.65	5.734%	$263.9649	$263.96	$263.95	$264.00
Purchase #5	$75.84	8.505%	$82.2902	$82.29	$82.30	$82.30
Purchase #6	$190.50	9.467%	$208.5346	$208.53	$208.55	$208.50
Purchase #7	$239.46	12.325%	$268.9734	$268.97	$268.95	$269.00
7 purchase totals =	$1,053.23		$1,156.8956	$1,156.89	$1,156.90	$1,157.00