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	$16.30	3.505%	$16.8713	$16.87	$16.85	$16.90
Purchase #2	$76.36	9.874%	$83.8998	$83.90	$83.90	$83.90
Purchase #3	$41.76	9.536%	$45.7422	$45.74	$45.75	$45.70
Purchase #4	$248.69	10.335%	$274.3921	$274.39	$274.40	$274.40
Purchase #5	$92.45	4.121%	$96.2599	$96.26	$96.25	$96.30
Purchase #6	$97.98	12.159%	$109.8934	$109.89	$109.90	$109.90
Purchase #7	$120.81	9.146%	$131.8593	$131.86	$131.85	$131.90
7 purchase totals =	$694.35		$758.9180	$758.91	$758.90	$759.00