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	$123.47	6.206%	$131.1325	$131.13	$131.15	$131.10
Purchase #2	$14.30	8.467%	$15.5108	$15.51	$15.50	$15.50
Purchase #3	$187.76	8.280%	$203.3065	$203.31	$203.30	$203.30
Purchase #4	$39.86	13.698%	$45.32	$45.32	$45.30	$45.30
Purchase #5	$141.39	12.375%	$158.887	$158.89	$158.90	$158.90
Purchase #6	$163.96	5.181%	$172.4548	$172.45	$172.45	$172.50
Purchase #7	$168.50	13.647%	$191.4952	$191.50	$191.50	$191.50
7 purchase totals =	$839.24		$918.1068	$918.11	$918.10	$918.10