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	$93.80	6.431%	$99.8323	$99.83	$99.85	$99.80
Purchase #2	$81.56	12.662%	$91.8871	$91.89	$91.90	$91.90
Purchase #3	$6.98	5.533%	$7.3662	$7.37	$7.35	$7.40
Purchase #4	$237.53	6.753%	$253.5704	$253.57	$253.55	$253.60
Purchase #5	$177.94	4.837%	$186.547	$186.55	$186.55	$186.50
Purchase #6	$52.86	12.420%	$59.4252	$59.43	$59.45	$59.40
Purchase #7	$125.54	12.400%	$141.107	$141.11	$141.10	$141.10
7 purchase totals =	$776.21		$839.7352	$839.75	$839.75	$839.70