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	$64.83	9.793%	$71.1788	$71.18	$71.20	$71.20
Purchase #2	$100.83	4.676%	$105.5448	$105.54	$105.55	$105.50
Purchase #3	$125.61	10.799%	$139.1746	$139.17	$139.15	$139.20
Purchase #4	$242.93	7.407%	$260.9238	$260.92	$260.90	$260.90
Purchase #5	$72.93	7.760%	$78.5894	$78.59	$78.60	$78.60
Purchase #6	$164.95	9.736%	$181.0095	$181.01	$181.00	$181.00
Purchase #7	$168.61	13.125%	$190.7401	$190.74	$190.75	$190.70
7 purchase totals =	$940.69		$1,027.1610	$1,027.15	$1,027.15	$1,027.10