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	$5.77	11.352%	$6.425	$6.43	$6.45	$6.40
Purchase #2	$76.33	11.520%	$85.1232	$85.12	$85.10	$85.10
Purchase #3	$216.98	3.647%	$224.8933	$224.89	$224.90	$224.90
Purchase #4	$122.40	7.416%	$131.4772	$131.48	$131.50	$131.50
Purchase #5	$152.37	6.736%	$162.6336	$162.63	$162.65	$162.60
Purchase #6	$123.63	6.576%	$131.7599	$131.76	$131.75	$131.80
Purchase #7	$99.64	5.547%	$105.167	$105.17	$105.15	$105.20
7 purchase totals =	$797.12		$847.4792	$847.48	$847.50	$847.50