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	$115.59	10.677%	$127.9315	$127.93	$127.95	$127.90
Purchase #2	$172.67	8.802%	$187.8684	$187.87	$187.85	$187.90
Purchase #3	$160.85	7.434%	$172.8076	$172.81	$172.80	$172.80
Purchase #4	$31.82	11.651%	$35.5273	$35.53	$35.55	$35.50
Purchase #5	$31.71	4.791%	$33.2292	$33.23	$33.25	$33.20
Purchase #6	$240.48	11.812%	$268.8855	$268.89	$268.90	$268.90
Purchase #7	$150.86	9.129%	$164.632	$164.63	$164.65	$164.60
7 purchase totals =	$903.98		$990.8815	$990.89	$990.95	$990.80