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	$84.37	4.647%	$88.2907	$88.29	$88.30	$88.30
Purchase #2	$140.57	10.398%	$155.1865	$155.19	$155.20	$155.20
Purchase #3	$169.52	9.233%	$185.1718	$185.17	$185.15	$185.20
Purchase #4	$37.89	5.681%	$40.0425	$40.04	$40.05	$40.00
Purchase #5	$160.83	3.867%	$167.0493	$167.05	$167.05	$167.00
Purchase #6	$91.44	12.447%	$102.8215	$102.82	$102.80	$102.80
Purchase #7	$77.80	10.485%	$85.9573	$85.96	$85.95	$86.00
7 purchase totals =	$762.42		$824.5196	$824.52	$824.50	$824.50