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	$25.26	12.163%	$28.3324	$28.33	$28.35	$28.30
Purchase #2	$27.59	4.275%	$28.7695	$28.77	$28.75	$28.80
Purchase #3	$179.32	4.652%	$187.662	$187.66	$187.65	$187.70
Purchase #4	$59.31	11.210%	$65.9587	$65.96	$65.95	$66.00
Purchase #5	$172.86	5.474%	$182.3224	$182.32	$182.30	$182.30
Purchase #6	$215.77	3.330%	$222.9551	$222.96	$222.95	$223.00
Purchase #7	$59.32	9.447%	$64.924	$64.92	$64.90	$64.90
7 purchase totals =	$739.43		$780.9241	$780.92	$780.85	$781.00