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	$181.79	3.664%	$188.4508	$188.45	$188.45	$188.50
Purchase #2	$52.65	13.617%	$59.8194	$59.82	$59.80	$59.80
Purchase #3	$177.46	10.154%	$195.4793	$195.48	$195.50	$195.50
Purchase #4	$38.28	12.629%	$43.1144	$43.11	$43.10	$43.10
Purchase #5	$196.54	13.532%	$223.1358	$223.14	$223.15	$223.10
Purchase #6	$98.88	4.507%	$103.3365	$103.34	$103.35	$103.30
Purchase #7	$45.82	5.169%	$48.1884	$48.19	$48.20	$48.20
7 purchase totals =	$791.42		$861.5246	$861.53	$861.55	$861.50