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	$49.86	3.307%	$51.5089	$51.51	$51.50	$51.50
Purchase #2	$239.52	9.193%	$261.5391	$261.54	$261.55	$261.50
Purchase #3	$98.55	6.327%	$104.7853	$104.79	$104.80	$104.80
Purchase #4	$34.68	9.322%	$37.9129	$37.91	$37.90	$37.90
Purchase #5	$127.89	5.226%	$134.5735	$134.57	$134.55	$134.60
Purchase #6	$176.63	6.474%	$188.065	$188.07	$188.05	$188.10
Purchase #7	$64.50	4.587%	$67.4586	$67.46	$67.45	$67.50
7 purchase totals =	$791.63		$845.8433	$845.85	$845.80	$845.90