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	$123.45	11.550%	$137.7085	$137.71	$137.70	$137.70
Purchase #2	$177.71	7.693%	$191.3812	$191.38	$191.40	$191.40
Purchase #3	$139.57	5.764%	$147.6148	$147.61	$147.60	$147.60
Purchase #4	$65.79	9.426%	$71.9914	$71.99	$72.00	$72.00
Purchase #5	$173.47	13.504%	$196.8954	$196.90	$196.90	$196.90
Purchase #6	$136.95	3.498%	$141.7405	$141.74	$141.75	$141.70
Purchase #7	$89.27	8.264%	$96.6473	$96.65	$96.65	$96.60
7 purchase totals =	$906.21		$983.9791	$983.98	$984.00	$983.90