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	$28.98	7.506%	$31.1552	$31.16	$31.15	$31.20
Purchase #2	$32.47	13.249%	$36.772	$36.77	$36.75	$36.80
Purchase #3	$64.64	13.523%	$73.3813	$73.38	$73.40	$73.40
Purchase #4	$179.34	11.549%	$200.052	$200.05	$200.05	$200.10
Purchase #5	$86.54	11.127%	$96.1693	$96.17	$96.15	$96.20
Purchase #6	$129.72	13.713%	$147.5085	$147.51	$147.50	$147.50
Purchase #7	$187.33	7.453%	$201.2917	$201.29	$201.30	$201.30
7 purchase totals =	$709.02		$786.3300	$786.33	$786.30	$786.50