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	$66.42	6.711%	$70.8774	$70.88	$70.90	$70.90
Purchase #2	$139.96	10.659%	$154.8783	$154.88	$154.90	$154.90
Purchase #3	$221.75	13.158%	$250.9279	$250.93	$250.95	$250.90
Purchase #4	$85.82	8.178%	$92.8384	$92.84	$92.85	$92.80
Purchase #5	$38.73	8.684%	$42.0933	$42.09	$42.10	$42.10
Purchase #6	$239.99	12.338%	$269.6	$269.60	$269.60	$269.60
Purchase #7	$179.33	11.666%	$200.2506	$200.25	$200.25	$200.30
7 purchase totals =	$972.00		$1,081.4659	$1,081.47	$1,081.55	$1,081.50