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	$131.31	3.504%	$135.9111	$135.91	$135.90	$135.90
Purchase #2	$246.36	11.814%	$275.465	$275.47	$275.45	$275.50
Purchase #3	$67.48	5.265%	$71.0328	$71.03	$71.05	$71.00
Purchase #4	$228.32	8.130%	$246.8824	$246.88	$246.90	$246.90
Purchase #5	$90.38	11.382%	$100.6671	$100.67	$100.65	$100.70
Purchase #6	$178.73	3.776%	$185.4788	$185.48	$185.50	$185.50
Purchase #7	$175.49	12.227%	$196.9472	$196.95	$196.95	$196.90
7 purchase totals =	$1,118.07		$1,212.3844	$1,212.39	$1,212.40	$1,212.40