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	$134.63	3.764%	$139.6975	$139.70	$139.70	$139.70
Purchase #2	$81.46	9.298%	$89.0342	$89.03	$89.05	$89.00
Purchase #3	$163.38	7.742%	$176.0289	$176.03	$176.05	$176.00
Purchase #4	$95.34	7.312%	$102.3113	$102.31	$102.30	$102.30
Purchase #5	$91.38	9.562%	$100.1178	$100.12	$100.10	$100.10
Purchase #6	$131.62	11.171%	$146.3233	$146.32	$146.30	$146.30
Purchase #7	$60.56	9.574%	$66.358	$66.36	$66.35	$66.40
7 purchase totals =	$758.37		$819.8710	$819.87	$819.85	$819.80