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	$246.77	10.177%	$271.8838	$271.88	$271.90	$271.90
Purchase #2	$42.43	13.170%	$48.018	$48.02	$48.00	$48.00
Purchase #3	$231.59	10.759%	$256.5068	$256.51	$256.50	$256.50
Purchase #4	$205.64	13.312%	$233.0148	$233.01	$233.00	$233.00
Purchase #5	$64.91	10.743%	$71.8833	$71.88	$71.90	$71.90
Purchase #6	$79.56	7.517%	$85.5405	$85.54	$85.55	$85.50
Purchase #7	$105.61	6.788%	$112.7788	$112.78	$112.80	$112.80
7 purchase totals =	$976.51		$1,079.6260	$1,079.62	$1,079.65	$1,079.60