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	$28.98	13.468%	$32.883	$32.88	$32.90	$32.90
Purchase #2	$239.32	7.810%	$258.0109	$258.01	$258.00	$258.00
Purchase #3	$63.89	13.216%	$72.3337	$72.33	$72.35	$72.30
Purchase #4	$135.29	11.310%	$150.5913	$150.59	$150.60	$150.60
Purchase #5	$213.71	11.193%	$237.6306	$237.63	$237.65	$237.60
Purchase #6	$81.86	9.373%	$89.5327	$89.53	$89.55	$89.50
Purchase #7	$115.95	4.302%	$120.9382	$120.94	$120.95	$120.90
7 purchase totals =	$879.00		$961.9204	$961.91	$962.00	$961.80