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	$86.39	3.405%	$89.3316	$89.33	$89.35	$89.30
Purchase #2	$212.64	11.173%	$236.3983	$236.40	$236.40	$236.40
Purchase #3	$30.50	7.657%	$32.8354	$32.84	$32.85	$32.80
Purchase #4	$193.87	13.398%	$219.8447	$219.84	$219.85	$219.80
Purchase #5	$45.93	11.240%	$51.0925	$51.09	$51.10	$51.10
Purchase #6	$88.87	3.298%	$91.8009	$91.80	$91.80	$91.80
Purchase #7	$184.47	6.484%	$196.431	$196.43	$196.45	$196.40
7 purchase totals =	$842.67		$917.7344	$917.73	$917.80	$917.60