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	$212.64	12.172%	$238.5225	$238.52	$238.50	$238.50
Purchase #2	$198.84	12.348%	$223.3928	$223.39	$223.40	$223.40
Purchase #3	$78.89	9.634%	$86.4903	$86.49	$86.50	$86.50
Purchase #4	$140.85	4.414%	$147.0671	$147.07	$147.05	$147.10
Purchase #5	$153.30	7.741%	$165.167	$165.17	$165.15	$165.20
Purchase #6	$67.71	12.474%	$76.1561	$76.16	$76.15	$76.20
Purchase #7	$147.98	3.533%	$153.2081	$153.21	$153.20	$153.20
7 purchase totals =	$1,000.21		$1,090.0039	$1,090.01	$1,089.95	$1,090.10