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	$65.89	7.818%	$71.0413	$71.04	$71.05	$71.00
Purchase #2	$203.96	10.475%	$225.3248	$225.32	$225.30	$225.30
Purchase #3	$6.54	9.473%	$7.1595	$7.16	$7.15	$7.20
Purchase #4	$189.40	10.532%	$209.3476	$209.35	$209.35	$209.30
Purchase #5	$75.72	12.305%	$85.0373	$85.04	$85.05	$85.00
Purchase #6	$166.86	3.342%	$172.4365	$172.44	$172.45	$172.40
Purchase #7	$38.79	10.208%	$42.7497	$42.75	$42.75	$42.70
7 purchase totals =	$747.16		$813.0967	$813.10	$813.10	$812.90