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	$68.91	13.321%	$78.0895	$78.09	$78.10	$78.10
Purchase #2	$157.78	8.579%	$171.3159	$171.32	$171.30	$171.30
Purchase #3	$157.90	10.777%	$174.9169	$174.92	$174.90	$174.90
Purchase #4	$24.77	9.166%	$27.0404	$27.04	$27.05	$27.00
Purchase #5	$234.83	3.627%	$243.3473	$243.35	$243.35	$243.30
Purchase #6	$31.50	3.742%	$32.6787	$32.68	$32.70	$32.70
Purchase #7	$199.82	9.320%	$218.4432	$218.44	$218.45	$218.40
7 purchase totals =	$875.51		$945.8319	$945.84	$945.85	$945.70