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	$28.67	3.165%	$29.5774	$29.58	$29.60	$29.60
Purchase #2	$141.76	10.672%	$156.8886	$156.89	$156.90	$156.90
Purchase #3	$180.34	4.529%	$188.5076	$188.51	$188.50	$188.50
Purchase #4	$236.49	12.213%	$265.3725	$265.37	$265.35	$265.40
Purchase #5	$79.58	3.750%	$82.5643	$82.56	$82.55	$82.60
Purchase #6	$80.36	7.562%	$86.4368	$86.44	$86.45	$86.40
Purchase #7	$37.29	3.303%	$38.5217	$38.52	$38.50	$38.50
7 purchase totals =	$784.49		$847.8689	$847.87	$847.85	$847.90