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	$95.54	4.557%	$99.8938	$99.89	$99.90	$99.90
Purchase #2	$160.31	4.500%	$167.524	$167.52	$167.50	$167.50
Purchase #3	$85.31	11.171%	$94.84	$94.84	$94.85	$94.80
Purchase #4	$86.27	13.166%	$97.6283	$97.63	$97.65	$97.60
Purchase #5	$81.80	13.296%	$92.6761	$92.68	$92.70	$92.70
Purchase #6	$85.69	7.192%	$91.8528	$91.85	$91.85	$91.90
Purchase #7	$159.86	6.671%	$170.5243	$170.52	$170.50	$170.50
7 purchase totals =	$754.78		$814.9393	$814.93	$814.95	$814.90