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	$40.72	3.846%	$42.2861	$42.29	$42.30	$42.30
Purchase #2	$105.79	9.214%	$115.5375	$115.54	$115.55	$115.50
Purchase #3	$94.59	3.329%	$97.7389	$97.74	$97.75	$97.70
Purchase #4	$30.37	6.537%	$32.3553	$32.36	$32.35	$32.40
Purchase #5	$151.66	13.223%	$171.714	$171.71	$171.70	$171.70
Purchase #6	$101.51	9.780%	$111.4377	$111.44	$111.45	$111.40
Purchase #7	$206.64	12.263%	$231.9803	$231.98	$232.00	$232.00
7 purchase totals =	$731.28		$803.0498	$803.06	$803.10	$803.00