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	$170.58	6.616%	$181.8656	$181.87	$181.85	$181.90
Purchase #2	$102.45	6.653%	$109.266	$109.27	$109.25	$109.30
Purchase #3	$63.88	5.511%	$67.4004	$67.40	$67.40	$67.40
Purchase #4	$192.91	9.239%	$210.733	$210.73	$210.75	$210.70
Purchase #5	$40.41	11.175%	$44.9258	$44.93	$44.95	$44.90
Purchase #6	$37.47	8.595%	$40.6905	$40.69	$40.70	$40.70
Purchase #7	$176.89	7.645%	$190.4132	$190.41	$190.40	$190.40
7 purchase totals =	$784.59		$845.2945	$845.30	$845.30	$845.30