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	$210.37	4.231%	$219.2708	$219.27	$219.25	$219.30
Purchase #2	$67.99	4.623%	$71.1332	$71.13	$71.15	$71.10
Purchase #3	$126.59	6.832%	$135.2386	$135.24	$135.25	$135.20
Purchase #4	$37.53	7.300%	$40.2697	$40.27	$40.25	$40.30
Purchase #5	$219.86	10.595%	$243.1542	$243.15	$243.15	$243.20
Purchase #6	$67.94	6.771%	$72.5402	$72.54	$72.55	$72.50
Purchase #7	$61.81	10.296%	$68.174	$68.17	$68.15	$68.20
7 purchase totals =	$792.09		$849.7807	$849.77	$849.75	$849.80