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	$123.32	3.497%	$127.6325	$127.63	$127.65	$127.60
Purchase #2	$102.74	7.330%	$110.2708	$110.27	$110.25	$110.30
Purchase #3	$123.53	10.811%	$136.8848	$136.88	$136.90	$136.90
Purchase #4	$227.26	6.711%	$242.5114	$242.51	$242.50	$242.50
Purchase #5	$55.38	10.465%	$61.1755	$61.18	$61.20	$61.20
Purchase #6	$52.53	6.468%	$55.9276	$55.93	$55.95	$55.90
Purchase #7	$203.78	11.481%	$227.176	$227.18	$227.20	$227.20
7 purchase totals =	$888.54		$961.5786	$961.58	$961.65	$961.60