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	$80.76	5.365%	$85.0928	$85.09	$85.10	$85.10
Purchase #2	$109.52	12.576%	$123.2932	$123.29	$123.30	$123.30
Purchase #3	$163.88	11.445%	$182.6361	$182.64	$182.65	$182.60
Purchase #4	$72.77	7.850%	$78.4824	$78.48	$78.50	$78.50
Purchase #5	$23.73	13.148%	$26.85	$26.85	$26.85	$26.90
Purchase #6	$8.60	3.152%	$8.8711	$8.87	$8.85	$8.90
Purchase #7	$43.32	5.595%	$45.7438	$45.74	$45.75	$45.70
7 purchase totals =	$502.58		$550.9694	$550.96	$551.00	$551.00