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	$22.85	10.789%	$25.3153	$25.32	$25.30	$25.30
Purchase #2	$220.73	8.818%	$240.194	$240.19	$240.20	$240.20
Purchase #3	$62.74	9.780%	$68.876	$68.88	$68.90	$68.90
Purchase #4	$85.50	4.452%	$89.3065	$89.31	$89.30	$89.30
Purchase #5	$81.51	9.657%	$89.3814	$89.38	$89.40	$89.40
Purchase #6	$237.42	8.645%	$257.945	$257.95	$257.95	$257.90
Purchase #7	$42.84	6.392%	$45.5783	$45.58	$45.60	$45.60
7 purchase totals =	$753.59		$816.5965	$816.61	$816.65	$816.60