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	$30.50	4.584%	$31.8981	$31.90	$31.90	$31.90
Purchase #2	$31.33	10.247%	$34.5404	$34.54	$34.55	$34.50
Purchase #3	$111.35	7.686%	$119.9084	$119.91	$119.90	$119.90
Purchase #4	$78.44	10.780%	$86.8958	$86.90	$86.90	$86.90
Purchase #5	$119.95	7.121%	$128.4916	$128.49	$128.50	$128.50
Purchase #6	$190.93	11.463%	$212.8163	$212.82	$212.80	$212.80
Purchase #7	$226.68	4.682%	$237.2932	$237.29	$237.30	$237.30
7 purchase totals =	$789.18		$851.8438	$851.85	$851.85	$851.80