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	$28.51	11.570%	$31.8086	$31.81	$31.80	$31.80
Purchase #2	$163.99	3.777%	$170.1839	$170.18	$170.20	$170.20
Purchase #3	$93.63	5.241%	$98.5371	$98.54	$98.55	$98.50
Purchase #4	$96.82	3.841%	$100.5389	$100.54	$100.55	$100.50
Purchase #5	$198.92	8.740%	$216.3056	$216.31	$216.30	$216.30
Purchase #6	$93.39	7.739%	$100.6175	$100.62	$100.60	$100.60
Purchase #7	$131.30	7.652%	$141.3471	$141.35	$141.35	$141.30
7 purchase totals =	$806.56		$859.3387	$859.35	$859.35	$859.20