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	$78.72	4.489%	$82.2537	$82.25	$82.25	$82.30
Purchase #2	$133.44	4.310%	$139.1913	$139.19	$139.20	$139.20
Purchase #3	$157.82	6.653%	$168.3198	$168.32	$168.30	$168.30
Purchase #4	$94.79	9.466%	$103.7628	$103.76	$103.75	$103.80
Purchase #5	$143.90	12.558%	$161.971	$161.97	$161.95	$162.00
Purchase #6	$205.49	9.449%	$224.9068	$224.91	$224.90	$224.90
Purchase #7	$35.49	13.656%	$40.3365	$40.34	$40.35	$40.30
7 purchase totals =	$849.65		$920.7419	$920.74	$920.70	$920.80