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	$98.96	13.309%	$112.1306	$112.13	$112.15	$112.10
Purchase #2	$178.49	8.701%	$194.0204	$194.02	$194.00	$194.00
Purchase #3	$90.36	13.587%	$102.6372	$102.64	$102.65	$102.60
Purchase #4	$136.87	11.446%	$152.5361	$152.54	$152.55	$152.50
Purchase #5	$78.27	5.267%	$82.3925	$82.39	$82.40	$82.40
Purchase #6	$111.43	5.409%	$117.4572	$117.46	$117.45	$117.50
Purchase #7	$159.43	3.280%	$164.6593	$164.66	$164.65	$164.70
7 purchase totals =	$853.81		$925.8333	$925.84	$925.85	$925.80