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	$109.46	12.576%	$123.2257	$123.23	$123.25	$123.20
Purchase #2	$214.54	8.856%	$233.5397	$233.54	$233.55	$233.50
Purchase #3	$167.53	10.540%	$185.1877	$185.19	$185.20	$185.20
Purchase #4	$78.82	8.741%	$85.7097	$85.71	$85.70	$85.70
Purchase #5	$43.81	9.835%	$48.1187	$48.12	$48.10	$48.10
Purchase #6	$142.25	3.197%	$146.7977	$146.80	$146.80	$146.80
Purchase #7	$73.57	11.728%	$82.1983	$82.20	$82.20	$82.20
7 purchase totals =	$829.98		$904.7775	$904.79	$904.80	$904.70