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	$163.64	4.549%	$171.084	$171.08	$171.10	$171.10
Purchase #2	$73.84	12.300%	$82.9223	$82.92	$82.90	$82.90
Purchase #3	$142.73	8.194%	$154.4253	$154.43	$154.45	$154.40
Purchase #4	$37.48	8.189%	$40.5492	$40.55	$40.55	$40.50
Purchase #5	$81.86	8.788%	$89.0539	$89.05	$89.05	$89.10
Purchase #6	$206.57	9.830%	$226.8758	$226.88	$226.90	$226.90
Purchase #7	$96.89	6.219%	$102.9156	$102.92	$102.90	$102.90
7 purchase totals =	$803.01		$867.8261	$867.83	$867.85	$867.80