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	$197.86	13.856%	$225.2755	$225.28	$225.30	$225.30
Purchase #2	$229.38	9.355%	$250.8385	$250.84	$250.85	$250.80
Purchase #3	$179.43	6.381%	$190.8794	$190.88	$190.90	$190.90
Purchase #4	$215.40	5.629%	$227.5249	$227.52	$227.50	$227.50
Purchase #5	$75.87	6.320%	$80.665	$80.67	$80.65	$80.70
Purchase #6	$127.74	11.436%	$142.3483	$142.35	$142.35	$142.30
Purchase #7	$139.81	11.816%	$156.3299	$156.33	$156.35	$156.30
7 purchase totals =	$1,165.49		$1,273.8615	$1,273.87	$1,273.90	$1,273.80