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	$67.61	10.774%	$74.8943	$74.89	$74.90	$74.90
Purchase #2	$135.31	3.715%	$140.3368	$140.34	$140.35	$140.30
Purchase #3	$142.98	9.406%	$156.4287	$156.43	$156.45	$156.40
Purchase #4	$31.48	12.780%	$35.5031	$35.50	$35.50	$35.50
Purchase #5	$236.76	5.615%	$250.0541	$250.05	$250.05	$250.10
Purchase #6	$56.84	9.497%	$62.2381	$62.24	$62.25	$62.20
Purchase #7	$172.86	13.680%	$196.5072	$196.51	$196.50	$196.50
7 purchase totals =	$843.84		$915.9623	$915.96	$916.00	$915.90