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	$152.82	7.786%	$164.7186	$164.72	$164.70	$164.70
Purchase #2	$108.56	4.481%	$113.4246	$113.42	$113.40	$113.40
Purchase #3	$147.74	6.140%	$156.8112	$156.81	$156.80	$156.80
Purchase #4	$118.39	4.722%	$123.9804	$123.98	$124.00	$124.00
Purchase #5	$6.92	13.869%	$7.8797	$7.88	$7.90	$7.90
Purchase #6	$38.76	4.586%	$40.5375	$40.54	$40.55	$40.50
Purchase #7	$24.41	4.770%	$25.5744	$25.57	$25.55	$25.60
7 purchase totals =	$597.60		$632.9264	$632.92	$632.90	$632.90