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	$86.37	3.201%	$89.1347	$89.13	$89.15	$89.10
Purchase #2	$191.54	11.489%	$213.546	$213.55	$213.55	$213.50
Purchase #3	$27.40	13.737%	$31.1639	$31.16	$31.15	$31.20
Purchase #4	$123.36	13.792%	$140.3738	$140.37	$140.35	$140.40
Purchase #5	$25.89	11.207%	$28.7915	$28.79	$28.80	$28.80
Purchase #6	$228.62	12.166%	$256.4339	$256.43	$256.45	$256.40
Purchase #7	$181.53	10.624%	$200.8157	$200.82	$200.80	$200.80
7 purchase totals =	$864.71		$960.2595	$960.25	$960.25	$960.20