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	$80.59	6.571%	$85.8856	$85.89	$85.90	$85.90
Purchase #2	$242.70	11.129%	$269.7101	$269.71	$269.70	$269.70
Purchase #3	$98.49	11.640%	$109.9542	$109.95	$109.95	$110.00
Purchase #4	$135.51	4.630%	$141.7841	$141.78	$141.80	$141.80
Purchase #5	$238.32	4.134%	$248.1721	$248.17	$248.15	$248.20
Purchase #6	$104.50	11.371%	$116.3827	$116.38	$116.40	$116.40
Purchase #7	$52.58	6.297%	$55.891	$55.89	$55.90	$55.90
7 purchase totals =	$952.69		$1,027.7798	$1,027.77	$1,027.80	$1,027.90