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	$62.45	5.501%	$65.8854	$65.89	$65.90	$65.90
Purchase #2	$182.50	11.280%	$203.086	$203.09	$203.10	$203.10
Purchase #3	$227.90	5.444%	$240.3069	$240.31	$240.30	$240.30
Purchase #4	$164.54	12.578%	$185.2358	$185.24	$185.25	$185.20
Purchase #5	$247.78	3.264%	$255.8675	$255.87	$255.85	$255.90
Purchase #6	$111.56	9.493%	$122.1504	$122.15	$122.15	$122.20
Purchase #7	$246.83	3.133%	$254.5632	$254.56	$254.55	$254.60
7 purchase totals =	$1,243.56		$1,327.0952	$1,327.11	$1,327.10	$1,327.20