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	$23.95	6.372%	$25.4761	$25.48	$25.50	$25.50
Purchase #2	$141.81	3.745%	$147.1208	$147.12	$147.10	$147.10
Purchase #3	$156.43	9.206%	$170.8309	$170.83	$170.85	$170.80
Purchase #4	$5.86	11.783%	$6.5505	$6.55	$6.55	$6.60
Purchase #5	$55.46	10.341%	$61.1951	$61.20	$61.20	$61.20
Purchase #6	$41.50	4.448%	$43.3459	$43.35	$43.35	$43.30
Purchase #7	$71.32	9.694%	$78.2338	$78.23	$78.25	$78.20
7 purchase totals =	$496.33		$532.7531	$532.76	$532.80	$532.70