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	$233.68	12.420%	$262.7031	$262.70	$262.70	$262.70
Purchase #2	$192.32	13.555%	$218.389	$218.39	$218.40	$218.40
Purchase #3	$13.48	7.574%	$14.501	$14.50	$14.50	$14.50
Purchase #4	$189.31	3.257%	$195.4758	$195.48	$195.50	$195.50
Purchase #5	$86.41	3.471%	$89.4093	$89.41	$89.40	$89.40
Purchase #6	$134.46	6.260%	$142.8772	$142.88	$142.90	$142.90
Purchase #7	$43.51	12.275%	$48.8509	$48.85	$48.85	$48.90
7 purchase totals =	$893.17		$972.2063	$972.21	$972.25	$972.30