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	$121.97	12.685%	$137.4419	$137.44	$137.45	$137.40
Purchase #2	$126.36	5.503%	$133.3136	$133.31	$133.30	$133.30
Purchase #3	$106.69	4.755%	$111.7631	$111.76	$111.75	$111.80
Purchase #4	$101.50	7.870%	$109.4881	$109.49	$109.50	$109.50
Purchase #5	$53.78	4.705%	$56.3103	$56.31	$56.30	$56.30
Purchase #6	$225.96	5.263%	$237.8523	$237.85	$237.85	$237.90
Purchase #7	$171.58	13.315%	$194.4259	$194.43	$194.45	$194.40
7 purchase totals =	$907.84		$980.5952	$980.59	$980.60	$980.60