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	$28.83	10.162%	$31.7597	$31.76	$31.75	$31.80
Purchase #2	$78.38	4.610%	$81.9933	$81.99	$82.00	$82.00
Purchase #3	$43.36	10.640%	$47.9735	$47.97	$47.95	$48.00
Purchase #4	$61.98	10.377%	$68.4117	$68.41	$68.40	$68.40
Purchase #5	$33.91	7.410%	$36.4227	$36.42	$36.40	$36.40
Purchase #6	$186.75	3.534%	$193.3497	$193.35	$193.35	$193.30
Purchase #7	$69.60	4.279%	$72.5782	$72.58	$72.60	$72.60
7 purchase totals =	$502.81		$532.4888	$532.48	$532.45	$532.50