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	$177.48	9.598%	$194.5145	$194.51	$194.50	$194.50
Purchase #2	$42.47	6.790%	$45.3537	$45.35	$45.35	$45.40
Purchase #3	$186.54	7.709%	$200.9204	$200.92	$200.90	$200.90
Purchase #4	$103.93	13.289%	$117.7413	$117.74	$117.75	$117.70
Purchase #5	$84.58	7.270%	$90.729	$90.73	$90.75	$90.70
Purchase #6	$95.34	8.369%	$103.319	$103.32	$103.30	$103.30
Purchase #7	$78.55	3.553%	$81.3409	$81.34	$81.35	$81.30
7 purchase totals =	$768.89		$833.9188	$833.91	$833.90	$833.80