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	$200.52	4.268%	$209.0782	$209.08	$209.10	$209.10
Purchase #2	$179.95	3.602%	$186.4318	$186.43	$186.45	$186.40
Purchase #3	$83.30	6.872%	$89.0244	$89.02	$89.00	$89.00
Purchase #4	$137.62	7.870%	$148.4507	$148.45	$148.45	$148.50
Purchase #5	$38.91	11.311%	$43.3111	$43.31	$43.30	$43.30
Purchase #6	$110.95	5.419%	$116.9624	$116.96	$116.95	$117.00
Purchase #7	$83.34	5.270%	$87.732	$87.73	$87.75	$87.70
7 purchase totals =	$834.59		$880.9906	$880.98	$881.00	$881.00