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	$33.96	9.398%	$37.1516	$37.15	$37.15	$37.20
Purchase #2	$245.46	8.307%	$265.8504	$265.85	$265.85	$265.90
Purchase #3	$129.25	9.777%	$141.8868	$141.89	$141.90	$141.90
Purchase #4	$231.73	13.858%	$263.8431	$263.84	$263.85	$263.80
Purchase #5	$177.78	11.784%	$198.7296	$198.73	$198.75	$198.70
Purchase #6	$80.47	11.787%	$89.955	$89.96	$89.95	$90.00
Purchase #7	$102.62	7.584%	$110.4027	$110.40	$110.40	$110.40
7 purchase totals =	$1,001.27		$1,107.8192	$1,107.82	$1,107.85	$1,107.90