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	$233.85	7.115%	$250.4884	$250.49	$250.50	$250.50
Purchase #2	$103.85	5.500%	$109.5618	$109.56	$109.55	$109.60
Purchase #3	$106.89	6.590%	$113.9341	$113.93	$113.95	$113.90
Purchase #4	$224.37	11.816%	$250.8816	$250.88	$250.90	$250.90
Purchase #5	$150.71	11.822%	$168.5269	$168.53	$168.55	$168.50
Purchase #6	$96.90	7.352%	$104.0241	$104.02	$104.00	$104.00
Purchase #7	$170.97	9.626%	$187.4276	$187.43	$187.45	$187.40
7 purchase totals =	$1,087.54		$1,184.8445	$1,184.84	$1,184.90	$1,184.80