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	$47.63	7.109%	$51.016	$51.02	$51.00	$51.00
Purchase #2	$242.69	13.266%	$274.8853	$274.89	$274.90	$274.90
Purchase #3	$49.81	5.484%	$52.5416	$52.54	$52.55	$52.50
Purchase #4	$39.95	4.361%	$41.6922	$41.69	$41.70	$41.70
Purchase #5	$152.79	13.406%	$173.273	$173.27	$173.25	$173.30
Purchase #6	$238.57	4.531%	$249.3796	$249.38	$249.40	$249.40
Purchase #7	$147.55	12.725%	$166.3257	$166.33	$166.35	$166.30
7 purchase totals =	$918.99		$1,009.1134	$1,009.12	$1,009.15	$1,009.10