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	$180.70	13.107%	$204.3843	$204.38	$204.40	$204.40
Purchase #2	$75.75	13.458%	$85.9444	$85.94	$85.95	$85.90
Purchase #3	$37.68	4.653%	$39.4333	$39.43	$39.45	$39.40
Purchase #4	$232.44	12.655%	$261.8553	$261.86	$261.85	$261.90
Purchase #5	$186.73	5.268%	$196.5669	$196.57	$196.55	$196.60
Purchase #6	$84.86	10.712%	$93.9502	$93.95	$93.95	$94.00
Purchase #7	$127.31	13.427%	$144.4039	$144.40	$144.40	$144.40
7 purchase totals =	$925.47		$1,026.5383	$1,026.53	$1,026.55	$1,026.60