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	$115.64	6.444%	$123.0918	$123.09	$123.10	$123.10
Purchase #2	$162.76	3.569%	$168.5689	$168.57	$168.55	$168.60
Purchase #3	$92.57	12.528%	$104.1672	$104.17	$104.15	$104.20
Purchase #4	$79.92	11.503%	$89.1132	$89.11	$89.10	$89.10
Purchase #5	$218.37	11.291%	$243.0262	$243.03	$243.05	$243.00
Purchase #6	$170.94	13.870%	$194.6494	$194.65	$194.65	$194.60
Purchase #7	$70.32	12.408%	$79.0453	$79.05	$79.05	$79.00
7 purchase totals =	$910.52		$1,001.6620	$1,001.67	$1,001.65	$1,001.60