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	$130.57	6.806%	$139.4566	$139.46	$139.45	$139.50
Purchase #2	$227.84	6.120%	$241.7838	$241.78	$241.80	$241.80
Purchase #3	$190.45	9.681%	$208.8875	$208.89	$208.90	$208.90
Purchase #4	$206.84	8.645%	$224.7213	$224.72	$224.70	$224.70
Purchase #5	$109.98	9.110%	$119.9992	$120.00	$120.00	$120.00
Purchase #6	$16.73	4.860%	$17.5431	$17.54	$17.55	$17.50
Purchase #7	$60.41	11.835%	$67.5595	$67.56	$67.55	$67.60
7 purchase totals =	$942.82		$1,019.9510	$1,019.95	$1,019.95	$1,020.00