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	$48.25	6.834%	$51.5474	$51.55	$51.55	$51.50
Purchase #2	$245.44	11.799%	$274.3995	$274.40	$274.40	$274.40
Purchase #3	$147.70	13.475%	$167.6026	$167.60	$167.60	$167.60
Purchase #4	$171.47	7.464%	$184.2685	$184.27	$184.25	$184.30
Purchase #5	$170.63	4.659%	$178.5797	$178.58	$178.60	$178.60
Purchase #6	$35.64	11.764%	$39.8327	$39.83	$39.85	$39.80
Purchase #7	$65.47	9.406%	$71.6281	$71.63	$71.65	$71.60
7 purchase totals =	$884.60		$967.8585	$967.86	$967.90	$967.80