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	$186.83	5.729%	$197.5335	$197.53	$197.55	$197.50
Purchase #2	$175.55	3.805%	$182.2297	$182.23	$182.25	$182.20
Purchase #3	$67.48	9.475%	$73.8737	$73.87	$73.85	$73.90
Purchase #4	$64.45	12.301%	$72.378	$72.38	$72.40	$72.40
Purchase #5	$71.89	11.412%	$80.0941	$80.09	$80.10	$80.10
Purchase #6	$133.94	5.681%	$141.5491	$141.55	$141.55	$141.50
Purchase #7	$75.46	9.398%	$82.5517	$82.55	$82.55	$82.60
7 purchase totals =	$775.60		$830.2098	$830.20	$830.25	$830.20