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	$79.30	8.284%	$85.8692	$85.87	$85.85	$85.90
Purchase #2	$170.79	9.639%	$187.2524	$187.25	$187.25	$187.30
Purchase #3	$249.36	12.671%	$280.9564	$280.96	$280.95	$281.00
Purchase #4	$28.86	12.300%	$32.4098	$32.41	$32.40	$32.40
Purchase #5	$131.27	7.176%	$140.6899	$140.69	$140.70	$140.70
Purchase #6	$98.81	13.601%	$112.2491	$112.25	$112.25	$112.20
Purchase #7	$151.86	3.676%	$157.4424	$157.44	$157.45	$157.40
7 purchase totals =	$910.25		$996.8692	$996.87	$996.85	$996.90