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	$180.52	5.841%	$191.0642	$191.06	$191.05	$191.10
Purchase #2	$250.31	12.260%	$280.998	$281.00	$281.00	$281.00
Purchase #3	$37.54	8.481%	$40.7238	$40.72	$40.70	$40.70
Purchase #4	$124.42	5.708%	$131.5219	$131.52	$131.50	$131.50
Purchase #5	$50.69	3.574%	$52.5017	$52.50	$52.50	$52.50
Purchase #6	$6.54	8.869%	$7.12	$7.12	$7.10	$7.10
Purchase #7	$82.34	12.592%	$92.7083	$92.71	$92.70	$92.70
7 purchase totals =	$732.36		$796.6379	$796.63	$796.55	$796.60