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	$25.79	11.322%	$28.7099	$28.71	$28.70	$28.70
Purchase #2	$242.26	13.588%	$275.1783	$275.18	$275.20	$275.20
Purchase #3	$135.95	4.116%	$141.5457	$141.55	$141.55	$141.50
Purchase #4	$59.98	13.123%	$67.8512	$67.85	$67.85	$67.90
Purchase #5	$125.36	12.572%	$141.1203	$141.12	$141.10	$141.10
Purchase #6	$148.98	13.466%	$169.0416	$169.04	$169.05	$169.00
Purchase #7	$105.61	3.537%	$109.3454	$109.35	$109.35	$109.30
7 purchase totals =	$843.93		$932.7924	$932.80	$932.80	$932.70