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	$76.79	12.538%	$86.4179	$86.42	$86.40	$86.40
Purchase #2	$41.78	5.417%	$44.0432	$44.04	$44.05	$44.00
Purchase #3	$114.73	3.622%	$118.8855	$118.89	$118.90	$118.90
Purchase #4	$102.61	8.601%	$111.4355	$111.44	$111.45	$111.40
Purchase #5	$86.45	9.315%	$94.5028	$94.50	$94.50	$94.50
Purchase #6	$133.55	12.625%	$150.4107	$150.41	$150.40	$150.40
Purchase #7	$180.47	12.155%	$202.4061	$202.41	$202.40	$202.40
7 purchase totals =	$736.38		$808.1017	$808.11	$808.10	$808.00