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	$89.89	9.646%	$98.5608	$98.56	$98.55	$98.60
Purchase #2	$144.59	10.252%	$159.4134	$159.41	$159.40	$159.40
Purchase #3	$6.67	12.120%	$7.4784	$7.48	$7.50	$7.50
Purchase #4	$68.80	4.690%	$72.0267	$72.03	$72.05	$72.00
Purchase #5	$110.84	9.106%	$120.9331	$120.93	$120.95	$120.90
Purchase #6	$68.69	5.567%	$72.514	$72.51	$72.50	$72.50
Purchase #7	$186.63	9.760%	$204.8451	$204.85	$204.85	$204.80
7 purchase totals =	$676.11		$735.7715	$735.77	$735.80	$735.70