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	$168.48	6.772%	$179.8895	$179.89	$179.90	$179.90
Purchase #2	$141.78	5.813%	$150.0217	$150.02	$150.00	$150.00
Purchase #3	$35.36	9.865%	$38.8483	$38.85	$38.85	$38.80
Purchase #4	$247.80	13.619%	$281.5479	$281.55	$281.55	$281.50
Purchase #5	$34.52	4.632%	$36.119	$36.12	$36.10	$36.10
Purchase #6	$33.78	7.391%	$36.2767	$36.28	$36.30	$36.30
Purchase #7	$151.90	12.499%	$170.886	$170.89	$170.90	$170.90
7 purchase totals =	$813.62		$893.5891	$893.60	$893.60	$893.50