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	$227.43	9.254%	$248.4764	$248.48	$248.50	$248.50
Purchase #2	$202.67	12.781%	$228.5733	$228.57	$228.55	$228.60
Purchase #3	$142.38	7.138%	$152.5431	$152.54	$152.55	$152.50
Purchase #4	$96.47	3.767%	$100.104	$100.10	$100.10	$100.10
Purchase #5	$115.61	11.733%	$129.1745	$129.17	$129.15	$129.20
Purchase #6	$236.54	10.737%	$261.9373	$261.94	$261.95	$261.90
Purchase #7	$173.94	3.489%	$180.0088	$180.01	$180.00	$180.00
7 purchase totals =	$1,195.04		$1,300.8174	$1,300.81	$1,300.80	$1,300.80