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	$78.96	4.726%	$82.6916	$82.69	$82.70	$82.70
Purchase #2	$46.31	13.276%	$52.4581	$52.46	$52.45	$52.50
Purchase #3	$122.59	6.502%	$130.5608	$130.56	$130.55	$130.60
Purchase #4	$36.26	11.787%	$40.534	$40.53	$40.55	$40.50
Purchase #5	$29.93	11.440%	$33.354	$33.35	$33.35	$33.40
Purchase #6	$239.31	3.376%	$247.3891	$247.39	$247.40	$247.40
Purchase #7	$204.41	13.441%	$231.8847	$231.88	$231.90	$231.90
7 purchase totals =	$757.77		$818.8723	$818.86	$818.90	$819.00