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	$178.90	6.456%	$190.4498	$190.45	$190.45	$190.40
Purchase #2	$40.99	3.589%	$42.4611	$42.46	$42.45	$42.50
Purchase #3	$240.96	13.540%	$273.586	$273.59	$273.60	$273.60
Purchase #4	$161.73	6.296%	$171.9125	$171.91	$171.90	$171.90
Purchase #5	$222.82	12.429%	$250.5143	$250.51	$250.50	$250.50
Purchase #6	$191.29	5.740%	$202.27	$202.27	$202.25	$202.30
Purchase #7	$154.43	11.352%	$171.9609	$171.96	$171.95	$172.00
7 purchase totals =	$1,191.12		$1,303.1546	$1,303.15	$1,303.10	$1,303.20