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	$93.34	7.400%	$100.2472	$100.25	$100.25	$100.20
Purchase #2	$165.39	12.497%	$186.0588	$186.06	$186.05	$186.10
Purchase #3	$31.86	13.592%	$36.1904	$36.19	$36.20	$36.20
Purchase #4	$179.84	5.874%	$190.4038	$190.40	$190.40	$190.40
Purchase #5	$150.94	9.836%	$165.7865	$165.79	$165.80	$165.80
Purchase #6	$167.61	7.148%	$179.5908	$179.59	$179.60	$179.60
Purchase #7	$170.53	6.333%	$181.3297	$181.33	$181.35	$181.30
7 purchase totals =	$959.51		$1,039.6072	$1,039.61	$1,039.65	$1,039.60