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	$137.40	7.597%	$147.8383	$147.84	$147.85	$147.80
Purchase #2	$82.48	8.246%	$89.2813	$89.28	$89.30	$89.30
Purchase #3	$209.29	3.431%	$216.4707	$216.47	$216.45	$216.50
Purchase #4	$217.77	12.281%	$244.5143	$244.51	$244.50	$244.50
Purchase #5	$178.94	13.383%	$202.8875	$202.89	$202.90	$202.90
Purchase #6	$25.93	7.128%	$27.7783	$27.78	$27.80	$27.80
Purchase #7	$66.30	11.175%	$73.709	$73.71	$73.70	$73.70
7 purchase totals =	$918.11		$1,002.4794	$1,002.48	$1,002.50	$1,002.50