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	$38.80	6.479%	$41.3139	$41.31	$41.30	$41.30
Purchase #2	$45.58	11.754%	$50.9375	$50.94	$50.95	$50.90
Purchase #3	$81.92	11.848%	$91.6259	$91.63	$91.65	$91.60
Purchase #4	$63.48	12.648%	$71.509	$71.51	$71.50	$71.50
Purchase #5	$242.85	6.198%	$257.9018	$257.90	$257.90	$257.90
Purchase #6	$169.49	7.411%	$182.0509	$182.05	$182.05	$182.10
Purchase #7	$105.71	7.414%	$113.5473	$113.55	$113.55	$113.50
7 purchase totals =	$747.83		$808.8863	$808.89	$808.90	$808.80