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	$37.92	11.807%	$42.3972	$42.40	$42.40	$42.40
Purchase #2	$173.92	6.534%	$185.2839	$185.28	$185.30	$185.30
Purchase #3	$79.97	7.605%	$86.0517	$86.05	$86.05	$86.10
Purchase #4	$147.85	11.198%	$164.4062	$164.41	$164.40	$164.40
Purchase #5	$121.85	9.148%	$132.9968	$133.00	$133.00	$133.00
Purchase #6	$222.83	10.154%	$245.4562	$245.46	$245.45	$245.50
Purchase #7	$90.59	6.362%	$96.3533	$96.35	$96.35	$96.40
7 purchase totals =	$874.93		$952.9453	$952.95	$952.95	$953.10