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	$31.49	7.780%	$33.9399	$33.94	$33.95	$33.90
Purchase #2	$220.40	12.277%	$247.4585	$247.46	$247.45	$247.50
Purchase #3	$78.73	6.266%	$83.6632	$83.66	$83.65	$83.70
Purchase #4	$224.32	11.404%	$249.9015	$249.90	$249.90	$249.90
Purchase #5	$75.29	7.767%	$81.1378	$81.14	$81.15	$81.10
Purchase #6	$250.30	3.832%	$259.8915	$259.89	$259.90	$259.90
Purchase #7	$35.52	13.458%	$40.3003	$40.30	$40.30	$40.30
7 purchase totals =	$916.05		$996.2927	$996.29	$996.30	$996.30