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	$29.31	7.412%	$31.4825	$31.48	$31.50	$31.50
Purchase #2	$104.33	12.341%	$117.2054	$117.21	$117.20	$117.20
Purchase #3	$68.37	4.607%	$71.5198	$71.52	$71.50	$71.50
Purchase #4	$179.78	11.248%	$200.0017	$200.00	$200.00	$200.00
Purchase #5	$226.27	9.859%	$248.578	$248.58	$248.60	$248.60
Purchase #6	$181.73	5.627%	$191.9559	$191.96	$191.95	$192.00
Purchase #7	$64.96	10.465%	$71.7581	$71.76	$71.75	$71.80
7 purchase totals =	$854.75		$932.5014	$932.51	$932.50	$932.60