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	$178.88	3.710%	$185.5164	$185.52	$185.50	$185.50
Purchase #2	$146.32	10.659%	$161.9162	$161.92	$161.90	$161.90
Purchase #3	$212.25	5.448%	$223.8134	$223.81	$223.80	$223.80
Purchase #4	$54.73	12.149%	$61.3791	$61.38	$61.40	$61.40
Purchase #5	$142.30	11.421%	$158.5521	$158.55	$158.55	$158.60
Purchase #6	$227.98	9.159%	$248.8607	$248.86	$248.85	$248.90
Purchase #7	$48.36	9.319%	$52.8667	$52.87	$52.85	$52.90
7 purchase totals =	$1,010.82		$1,092.9046	$1,092.91	$1,092.85	$1,093.00