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	$76.74	12.289%	$86.1706	$86.17	$86.15	$86.20
Purchase #2	$239.56	6.370%	$254.82	$254.82	$254.80	$254.80
Purchase #3	$109.42	12.819%	$123.4465	$123.45	$123.45	$123.40
Purchase #4	$119.64	3.575%	$123.9171	$123.92	$123.90	$123.90
Purchase #5	$195.71	9.195%	$213.7055	$213.71	$213.70	$213.70
Purchase #6	$126.89	11.804%	$141.8681	$141.87	$141.85	$141.90
Purchase #7	$122.57	5.107%	$128.8296	$128.83	$128.85	$128.80
7 purchase totals =	$990.53		$1,072.7574	$1,072.77	$1,072.70	$1,072.70